diff --git a/src/drivers/spi/spi_flash.c b/src/drivers/spi/spi_flash.c
index b2fdab9f2d..b6d535a71a 100644
--- a/src/drivers/spi/spi_flash.c
+++ b/src/drivers/spi/spi_flash.c
@@ -48,8 +48,8 @@ static void spi_flash_addr(u32 addr, u8 *cmd)
  * FIXME: This really should be abstracted better, but that will
  * require overhauling the entire SPI infrastructure.
  */
-static int do_spi_flash_cmd(struct spi_slave *spi, const void *dout,
-		unsigned int bytes_out, void *din, unsigned int bytes_in)
+static int do_spi_flash_cmd(const struct spi_slave *spi, const void *dout,
+			    size_t bytes_out, void *din, size_t bytes_in)
 {
 	int ret = 1;
 
diff --git a/src/drivers/spi/tpm/tpm.c b/src/drivers/spi/tpm/tpm.c
index 9651ea8387..d364cb958a 100644
--- a/src/drivers/spi/tpm/tpm.c
+++ b/src/drivers/spi/tpm/tpm.c
@@ -37,11 +37,11 @@
 /* SPI Interface descriptor used by the driver. */
 struct tpm_spi_if {
 	struct spi_slave *slave;
-	int (*cs_assert)(struct spi_slave *slave);
-	void (*cs_deassert)(struct spi_slave *slave);
-	int  (*xfer)(struct spi_slave *slave, const void *dout,
-		     unsigned bytesout, void *din,
-		     unsigned bytesin);
+	int (*cs_assert)(const struct spi_slave *slave);
+	void (*cs_deassert)(const struct spi_slave *slave);
+	int  (*xfer)(const struct spi_slave *slave, const void *dout,
+		     size_t bytesout, void *din,
+		     size_t bytesin);
 };
 
 /* Use the common SPI driver wrapper as the interface callbacks. */
diff --git a/src/include/spi-generic.h b/src/include/spi-generic.h
index 347ec3c202..7c53611d79 100644
--- a/src/include/spi-generic.h
+++ b/src/include/spi-generic.h
@@ -17,6 +17,7 @@
 #define _SPI_GENERIC_H_
 
 #include <stdint.h>
+#include <stddef.h>
 
 /* Controller-specific definitions: */
 
@@ -67,7 +68,7 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs);
  * Returns: 0 if the bus was claimed successfully, or a negative value
  * if it wasn't.
  */
-int spi_claim_bus(struct spi_slave *slave);
+int spi_claim_bus(const struct spi_slave *slave);
 
 /*-----------------------------------------------------------------------
  * Release the SPI bus
@@ -78,7 +79,7 @@ int spi_claim_bus(struct spi_slave *slave);
  *
  *   slave:	The SPI slave
  */
-void spi_release_bus(struct spi_slave *slave);
+void spi_release_bus(const struct spi_slave *slave);
 
 /*-----------------------------------------------------------------------
  * SPI transfer
@@ -92,10 +93,8 @@ void spi_release_bus(struct spi_slave *slave);
  *
  *   Returns: 0 on success, not 0 on failure
  */
-int  spi_xfer(struct spi_slave *slave, const void *dout, unsigned int bytesout,
-		void *din, unsigned int bytesin);
-
-
+int spi_xfer(const struct spi_slave *slave, const void *dout, size_t bytesout,
+	     void *din, size_t bytesin);
 
 unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len);
 
@@ -108,7 +107,7 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len);
  *
  * TODO: This function probably shouldn't be inlined.
  */
-static inline int spi_w8r8(struct spi_slave *slave, unsigned char byte)
+static inline int spi_w8r8(const struct spi_slave *slave, unsigned char byte)
 {
 	unsigned char dout[2];
 	unsigned char din[2];
diff --git a/src/soc/broadcom/cygnus/spi.c b/src/soc/broadcom/cygnus/spi.c
index d7c0a8d4a6..13b69765b2 100644
--- a/src/soc/broadcom/cygnus/spi.c
+++ b/src/soc/broadcom/cygnus/spi.c
@@ -156,7 +156,7 @@ static int mspi_enable(struct qspi_priv *priv)
 	return 0;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	struct qspi_priv *priv = to_qspi_slave(slave);
 
@@ -175,7 +175,7 @@ int spi_claim_bus(struct spi_slave *slave)
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct qspi_priv *priv = to_qspi_slave(slave);
 
@@ -189,8 +189,8 @@ void spi_release_bus(struct spi_slave *slave)
 #define RXRAM_8B(p, i)	(REG_RD((p)->reg + MSPI_RXRAM_REG + \
 				((((i) << 1) + 1) << 2)) & 0xff)
 
-int spi_xfer(struct spi_slave *slave, const void *dout, unsigned int bytesout,
-	     void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout, size_t bytesout,
+	     void *din, size_t bytesin)
 {
 	struct qspi_priv *priv = to_qspi_slave(slave);
 	const u8 *tx = (const u8 *)dout;
diff --git a/src/soc/imgtec/pistachio/spi.c b/src/soc/imgtec/pistachio/spi.c
index 2b4b01c3a7..307aec9ec8 100644
--- a/src/soc/imgtec/pistachio/spi.c
+++ b/src/soc/imgtec/pistachio/spi.c
@@ -60,7 +60,7 @@ static int wait_status(u32 reg, u32 shift)
 }
 
 /* Transmitter function. Fills TX FIFO with data before enabling SPIM */
-static int transmitdata(struct spi_slave *slave, u8 *buffer, u32 size)
+static int transmitdata(const struct spi_slave *slave, u8 *buffer, u32 size)
 {
 	u32 blocksize, base, write_data;
 	int ret;
@@ -97,7 +97,7 @@ static int transmitdata(struct spi_slave *slave, u8 *buffer, u32 size)
 }
 
 /* Receiver function */
-static int receivedata(struct spi_slave *slave, u8 *buffer, u32 size)
+static int receivedata(const struct spi_slave *slave, u8 *buffer, u32 size)
 {
 	u32 read_data, base;
 	int ret;
@@ -141,7 +141,7 @@ static int receivedata(struct spi_slave *slave, u8 *buffer, u32 size)
 }
 
 /* Sets port parameters in port state register. */
-static void  setparams(struct spi_slave *slave, u32 port,
+static void  setparams(const struct spi_slave *slave, u32 port,
 			struct spim_device_parameters *params)
 {
 	u32 spim_parameters, port_state, base;
@@ -247,7 +247,7 @@ static u32 control_reg_setup(struct spim_buffer *first,
 }
 
 /* Checks the given buffer information */
-static int check_buffers(struct spi_slave *slave, struct spim_buffer *first,
+static int check_buffers(const struct spi_slave *slave, struct spim_buffer *first,
 				struct spim_buffer *second){
 
 	if (!(container_of(slave, struct img_spi_slave, slave)->initialised))
@@ -325,7 +325,7 @@ static int check_device_params(struct spim_device_parameters *pdev_param)
 }
 
 /* Function that carries out read/write operations */
-static int spim_io(struct spi_slave *slave, struct spim_buffer *first,
+static int spim_io(const struct spi_slave *slave, struct spim_buffer *first,
 			struct spim_buffer *second)
 {
 	u32 reg, base;
@@ -459,7 +459,7 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs)
 }
 
 /* Claim the bus and prepare it for communication */
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	int ret;
 	struct img_spi_slave *img_slave;
@@ -490,7 +490,7 @@ int spi_claim_bus(struct spi_slave *slave)
 }
 
 /* Release the SPI bus */
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct img_spi_slave *img_slave;
 
@@ -508,8 +508,8 @@ void spi_release_bus(struct spi_slave *slave)
 }
 
 /* SPI transfer */
-static int do_spi_xfer(struct spi_slave *slave, const void *dout,
-		       unsigned int bytesout, void *din, unsigned int bytesin)
+static int do_spi_xfer(const struct spi_slave *slave, const void *dout,
+		       size_t bytesout, void *din, size_t bytesin)
 {
 	struct spim_buffer	buff_0;
 	struct spim_buffer	buff_1;
@@ -532,8 +532,8 @@ static int do_spi_xfer(struct spi_slave *slave, const void *dout,
 	return spim_io(slave, &buff_0, (dout && din) ? &buff_1 : NULL);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout, unsigned int bytesout,
-	     void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout, size_t bytesout,
+	     void *din, size_t bytesin)
 {
 	unsigned int in_sz, out_sz;
 	int ret;
diff --git a/src/soc/intel/apollolake/spi.c b/src/soc/intel/apollolake/spi.c
index eab3a12eac..6e873f45c8 100644
--- a/src/soc/intel/apollolake/spi.c
+++ b/src/soc/intel/apollolake/spi.c
@@ -184,8 +184,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return MIN(buf_len, SPIBAR_FDATA_FIFO_SIZE);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+	     size_t bytesout, void *din, size_t bytesin)
 {
 	printk(BIOS_DEBUG, "NOT IMPLEMENTED: %s() !!!\n", __func__);
 	return E_NOT_IMPLEMENTED;
@@ -215,13 +215,13 @@ void spi_init(void)
 	pci_write_config32(ctx->pci_dev, SPIBAR_BIOS_CONTROL, bios_ctl);
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* There's nothing we need to to here. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* No magic needed here. */
 }
diff --git a/src/soc/intel/baytrail/spi.c b/src/soc/intel/baytrail/spi.c
index 1f2b285b93..13f88067eb 100644
--- a/src/soc/intel/baytrail/spi.c
+++ b/src/soc/intel/baytrail/spi.c
@@ -317,13 +317,13 @@ static void spi_init_cb(void *unused)
 
 BOOT_STATE_INIT_ENTRY(BS_DEV_INIT, BS_ON_ENTRY, spi_init_cb, NULL);
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 }
@@ -489,8 +489,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(cntlr.databytes, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	uint16_t control;
 	int16_t opcode_index;
diff --git a/src/soc/intel/braswell/spi.c b/src/soc/intel/braswell/spi.c
index 01f215008d..34e031b1cd 100644
--- a/src/soc/intel/braswell/spi.c
+++ b/src/soc/intel/braswell/spi.c
@@ -296,13 +296,13 @@ static void spi_init_cb(void *unused)
 
 BOOT_STATE_INIT_ENTRY(BS_DEV_INIT, BS_ON_ENTRY, spi_init_cb, NULL);
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 }
@@ -470,8 +470,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(cntlr.databytes, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	uint16_t control;
 	int16_t opcode_index;
diff --git a/src/soc/intel/broadwell/spi.c b/src/soc/intel/broadwell/spi.c
index c7ac09c7de..6aa7dd33a8 100644
--- a/src/soc/intel/broadwell/spi.c
+++ b/src/soc/intel/broadwell/spi.c
@@ -313,13 +313,13 @@ static void spi_init_cb(void *unused)
 
 BOOT_STATE_INIT_ENTRY(BS_DEV_INIT, BS_ON_ENTRY, spi_init_cb, NULL);
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 }
@@ -485,8 +485,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(cntlr.databytes, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	uint16_t control;
 	int16_t opcode_index;
diff --git a/src/soc/intel/fsp_baytrail/spi.c b/src/soc/intel/fsp_baytrail/spi.c
index 1ab73f3ae3..232366c63b 100644
--- a/src/soc/intel/fsp_baytrail/spi.c
+++ b/src/soc/intel/fsp_baytrail/spi.c
@@ -297,13 +297,13 @@ void spi_init(void)
 	cntlr.preop = &ich9_spi->preop;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 }
@@ -469,8 +469,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(cntlr.databytes, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	uint16_t control;
 	int16_t opcode_index;
diff --git a/src/soc/intel/fsp_broadwell_de/spi.c b/src/soc/intel/fsp_broadwell_de/spi.c
index 116001f010..c38fbce7b7 100644
--- a/src/soc/intel/fsp_broadwell_de/spi.c
+++ b/src/soc/intel/fsp_broadwell_de/spi.c
@@ -312,13 +312,13 @@ void spi_init(void)
 	pci_write_config_byte(dev, 0xdc, bios_cntl | 0x1);
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 }
@@ -484,8 +484,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(cntlr.databytes, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	uint16_t control;
 	int16_t opcode_index;
diff --git a/src/soc/intel/skylake/flash_controller.c b/src/soc/intel/skylake/flash_controller.c
index cc6c20a4be..8aee796218 100644
--- a/src/soc/intel/skylake/flash_controller.c
+++ b/src/soc/intel/skylake/flash_controller.c
@@ -151,8 +151,8 @@ static size_t spi_get_flash_size(pch_spi_regs *spi_bar)
 	return size;
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	/* TODO: Define xfer for hardware sequencing. */
 	return -1;
@@ -170,13 +170,13 @@ void spi_init(void)
 	pci_write_config_byte(dev, SPIBAR_BIOS_CNTL, bios_cntl);
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by PCH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by PCH automatically. */
 }
diff --git a/src/soc/marvell/armada38x/spi.c b/src/soc/marvell/armada38x/spi.c
index 6a0e062327..af0a279133 100644
--- a/src/soc/marvell/armada38x/spi.c
+++ b/src/soc/marvell/armada38x/spi.c
@@ -409,8 +409,8 @@ int mv_spi_8bit_data_tx_rx(unsigned char spi_id,
 	return MV_OK;
 }
 
-static int mrvl_spi_xfer(struct spi_slave *slave,
-			 unsigned int bitlen,
+static int mrvl_spi_xfer(const struct spi_slave *slave,
+			 size_t bitlen,
 			 const void *dout,
 			 void *din)
 {
@@ -454,14 +454,14 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs)
 	return slave;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	mv_spi_cs_set(slave->bus, slave->cs);
 	mv_spi_cs_assert(slave->bus);
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	mv_spi_cs_deassert(slave->bus);
 }
@@ -471,11 +471,11 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return buf_len;
 }
 
-int spi_xfer(struct spi_slave *slave,
+int spi_xfer(const struct spi_slave *slave,
 	     const void *dout,
-	     unsigned out_bytes,
+	     size_t out_bytes,
 	     void *din,
-	     unsigned in_bytes)
+	     size_t in_bytes)
 {
 	int ret = -1;
 
diff --git a/src/soc/marvell/bg4cd/spi.c b/src/soc/marvell/bg4cd/spi.c
index 53f46c78ec..9a999b049c 100644
--- a/src/soc/marvell/bg4cd/spi.c
+++ b/src/soc/marvell/bg4cd/spi.c
@@ -20,17 +20,17 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs)
 	return NULL;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-	     unsigned out_bytes, void *din, unsigned in_bytes)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+	     size_t out_bytes, void *din, size_t in_bytes)
 {
 	return 0;
 }
diff --git a/src/soc/mediatek/mt8173/spi.c b/src/soc/mediatek/mt8173/spi.c
index 9d56b63027..f60de6c32b 100644
--- a/src/soc/mediatek/mt8173/spi.c
+++ b/src/soc/mediatek/mt8173/spi.c
@@ -55,7 +55,7 @@ static struct mtk_spi_bus spi_bus[1] = {
 	}
 };
 
-static inline struct mtk_spi_bus *to_mtk_spi(struct spi_slave *slave)
+static inline struct mtk_spi_bus *to_mtk_spi(const struct spi_slave *slave)
 {
 	return container_of(slave, struct mtk_spi_bus, slave);
 }
@@ -182,7 +182,7 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs)
 	};
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	struct mtk_spi_bus *mtk_slave = to_mtk_spi(slave);
 	struct mtk_spi_regs *regs = mtk_slave->regs;
@@ -193,8 +193,8 @@ int spi_claim_bus(struct spi_slave *slave)
 	return 0;
 }
 
-static int mtk_spi_fifo_transfer(struct spi_slave *slave, void *in,
-				 const void *out, u32 size)
+static int mtk_spi_fifo_transfer(const struct spi_slave *slave, void *in,
+				 const void *out, size_t size)
 {
 	struct mtk_spi_bus *mtk_slave = to_mtk_spi(slave);
 	struct mtk_spi_regs *regs = mtk_slave->regs;
@@ -269,10 +269,10 @@ error:
 	return -1;
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout, unsigned int bytes_out,
-	     void *din, unsigned int bytes_in)
+int spi_xfer(const struct spi_slave *slave, const void *dout, size_t bytes_out,
+	     void *din, size_t bytes_in)
 {
-	uint32_t min_size = 0;
+	size_t min_size = 0;
 	int ret;
 
 	while (bytes_out || bytes_in) {
@@ -301,7 +301,7 @@ int spi_xfer(struct spi_slave *slave, const void *dout, unsigned int bytes_out,
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct mtk_spi_bus *mtk_slave = to_mtk_spi(slave);
 	struct mtk_spi_regs *regs = mtk_slave->regs;
diff --git a/src/soc/nvidia/tegra124/spi.c b/src/soc/nvidia/tegra124/spi.c
index d5be4a6034..2ad4aa1f85 100644
--- a/src/soc/nvidia/tegra124/spi.c
+++ b/src/soc/nvidia/tegra124/spi.c
@@ -209,7 +209,7 @@ static unsigned int tegra_spi_speed(unsigned int bus)
 	return 50000000;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	struct tegra_spi_regs *regs = to_tegra_spi(slave->bus)->regs;
 	u32 val;
@@ -232,7 +232,7 @@ int spi_claim_bus(struct spi_slave *slave)
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct tegra_spi_regs *regs = to_tegra_spi(slave->bus)->regs;
 	u32 val;
@@ -719,13 +719,13 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return buf_len;
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int out_bytes, void *din, unsigned int in_bytes)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+	     size_t out_bytes, void *din, size_t in_bytes)
 {
 	struct tegra_spi_channel *spi = to_tegra_spi(slave->bus);
 	u8 *out_buf = (u8 *)dout;
 	u8 *in_buf = (u8 *)din;
-	unsigned int todo;
+	size_t todo;
 	int ret = 0;
 
 	/* tegra bus numbers start at 1 */
diff --git a/src/soc/nvidia/tegra210/spi.c b/src/soc/nvidia/tegra210/spi.c
index b01289c3eb..7efefc44fe 100644
--- a/src/soc/nvidia/tegra210/spi.c
+++ b/src/soc/nvidia/tegra210/spi.c
@@ -208,7 +208,7 @@ static struct tegra_spi_channel * const to_tegra_spi(int bus) {
 	return &tegra_spi_channels[bus - 1];
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	struct tegra_spi_regs *regs = to_tegra_spi(slave->bus)->regs;
 	u32 val;
@@ -231,7 +231,7 @@ int spi_claim_bus(struct spi_slave *slave)
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct tegra_spi_regs *regs = to_tegra_spi(slave->bus)->regs;
 	u32 val;
@@ -755,13 +755,13 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return buf_len;
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int out_bytes, void *din, unsigned int in_bytes)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+	     size_t out_bytes, void *din, size_t in_bytes)
 {
 	struct tegra_spi_channel *spi = to_tegra_spi(slave->bus);
 	u8 *out_buf = (u8 *)dout;
 	u8 *in_buf = (u8 *)din;
-	unsigned int todo;
+	size_t todo;
 	int ret = 0;
 
 	/* tegra bus numbers start at 1 */
@@ -827,8 +827,8 @@ int spi_xfer(struct spi_slave *slave, const void *dout,
 
 	if (ret < 0) {
 		printk(BIOS_ERR, "%s: Error detected\n", __func__);
-		printk(BIOS_ERR, "Transaction size: %u, bytes remaining: "
-				"%u out / %u in\n", todo, out_bytes, in_bytes);
+		printk(BIOS_ERR, "Transaction size: %zu, bytes remaining: "
+				"%zu out / %zu in\n", todo, out_bytes, in_bytes);
 		clear_fifo_status(spi);
 	}
 	return ret;
diff --git a/src/soc/qualcomm/ipq40xx/include/soc/spi.h b/src/soc/qualcomm/ipq40xx/include/soc/spi.h
index 1fd6a571ca..8ef1fbf69d 100644
--- a/src/soc/qualcomm/ipq40xx/include/soc/spi.h
+++ b/src/soc/qualcomm/ipq40xx/include/soc/spi.h
@@ -186,7 +186,7 @@ struct ipq_spi_slave {
 	int allocated;
 };
 
-static inline struct ipq_spi_slave *to_ipq_spi(struct spi_slave *slave)
+static inline struct ipq_spi_slave *to_ipq_spi(const struct spi_slave *slave)
 {
 	return container_of(slave, struct ipq_spi_slave, slave);
 }
diff --git a/src/soc/qualcomm/ipq40xx/spi.c b/src/soc/qualcomm/ipq40xx/spi.c
index dcd00c0065..871f24b254 100644
--- a/src/soc/qualcomm/ipq40xx/spi.c
+++ b/src/soc/qualcomm/ipq40xx/spi.c
@@ -320,7 +320,7 @@ static int spi_hw_init(struct ipq_spi_slave *ds)
 	return SUCCESS;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	struct ipq_spi_slave *ds = to_ipq_spi(slave);
 	unsigned int ret;
@@ -332,7 +332,7 @@ int spi_claim_bus(struct spi_slave *slave)
 	return SUCCESS;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct ipq_spi_slave *ds = to_ipq_spi(slave);
 
@@ -341,7 +341,7 @@ void spi_release_bus(struct spi_slave *slave)
 	ds->initialized = 0;
 }
 
-static void write_force_cs(struct spi_slave *slave, int assert)
+static void write_force_cs(const struct spi_slave *slave, int assert)
 {
 	struct ipq_spi_slave *ds = to_ipq_spi(slave);
 
@@ -633,8 +633,8 @@ static int blsp_spi_write(struct ipq_spi_slave *ds, u8 *cmd_buffer,
  * This function is invoked with either tx_buf or rx_buf.
  * Calling this function with both null does a chip select change.
  */
-int spi_xfer(struct spi_slave *slave, const void *dout,
-	     unsigned out_bytes, void *din, unsigned in_bytes)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+	     size_t out_bytes, void *din, size_t in_bytes)
 {
 	struct ipq_spi_slave *ds = to_ipq_spi(slave);
 	u8 *txp = (u8 *)dout;
diff --git a/src/soc/qualcomm/ipq806x/include/soc/spi.h b/src/soc/qualcomm/ipq806x/include/soc/spi.h
index 4f6f055e61..5dedcdafba 100644
--- a/src/soc/qualcomm/ipq806x/include/soc/spi.h
+++ b/src/soc/qualcomm/ipq806x/include/soc/spi.h
@@ -271,7 +271,7 @@ struct ipq_spi_slave {
 	int allocated;
 };
 
-static inline struct ipq_spi_slave *to_ipq_spi(struct spi_slave *slave)
+static inline struct ipq_spi_slave *to_ipq_spi(const struct spi_slave *slave)
 {
 	return container_of(slave, struct ipq_spi_slave, slave);
 }
diff --git a/src/soc/qualcomm/ipq806x/spi.c b/src/soc/qualcomm/ipq806x/spi.c
index 71a8c29085..d1af7201fa 100644
--- a/src/soc/qualcomm/ipq806x/spi.c
+++ b/src/soc/qualcomm/ipq806x/spi.c
@@ -618,7 +618,7 @@ static int spi_hw_init(struct ipq_spi_slave *ds)
 	return SUCCESS;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	struct ipq_spi_slave *ds = to_ipq_spi(slave);
 	unsigned int ret;
@@ -641,7 +641,7 @@ int spi_claim_bus(struct spi_slave *slave)
 	return SUCCESS;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct ipq_spi_slave *ds = to_ipq_spi(slave);
 
@@ -711,8 +711,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(MAX_PACKET_COUNT, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-	     unsigned out_bytes, void *din, unsigned in_bytes)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+	     size_t out_bytes, void *din, size_t in_bytes)
 {
 	int ret;
 	struct ipq_spi_slave *ds = to_ipq_spi(slave);
diff --git a/src/soc/rockchip/common/spi.c b/src/soc/rockchip/common/spi.c
index 3666de39d1..8f45679dfc 100644
--- a/src/soc/rockchip/common/spi.c
+++ b/src/soc/rockchip/common/spi.c
@@ -68,7 +68,7 @@ static struct rockchip_spi_slave rockchip_spi_slaves[] = {
 #endif
 };
 
-static struct rockchip_spi_slave *to_rockchip_spi(struct spi_slave *slave)
+static struct rockchip_spi_slave *to_rockchip_spi(const struct spi_slave *slave)
 {
 	return container_of(slave, struct rockchip_spi_slave, slave);
 }
@@ -79,13 +79,13 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs)
 	return &(rockchip_spi_slaves[bus].slave);
 }
 
-static void spi_cs_activate(struct spi_slave *slave)
+static void spi_cs_activate(const struct spi_slave *slave)
 {
 	struct rockchip_spi *regs = to_rockchip_spi(slave)->regs;
 	setbits_le32(&regs->ser, 1);
 }
 
-static void spi_cs_deactivate(struct spi_slave *slave)
+static void spi_cs_deactivate(const struct spi_slave *slave)
 {
 	struct rockchip_spi *regs = to_rockchip_spi(slave)->regs;
 	clrbits_le32(&regs->ser, 1);
@@ -157,13 +157,13 @@ void rockchip_spi_set_sample_delay(unsigned int bus, unsigned int delay_ns)
 			rsd << SPI_RXDSD_OFFSET);
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	spi_cs_activate(slave);
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	spi_cs_deactivate(slave);
 }
@@ -203,11 +203,11 @@ static void set_transfer_mode(struct rockchip_spi *regs,
 
 /* returns 0 to indicate success, <0 otherwise */
 static int do_xfer(struct rockchip_spi *regs, bool use_16bit, const void *dout,
-		   unsigned int *bytes_out, void *din, unsigned int *bytes_in)
+		   size_t *bytes_out, void *din, size_t *bytes_in)
 {
 	uint8_t *in_buf = din;
 	uint8_t *out_buf = (uint8_t *)dout;
-	unsigned int min_xfer;
+	size_t min_xfer;
 
 	if (*bytes_out == 0)
 		min_xfer = *bytes_in;
@@ -268,8 +268,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(65535, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytes_out, void *din, unsigned int bytes_in)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytes_out, void *din, size_t bytes_in)
 {
 	struct rockchip_spi *regs = to_rockchip_spi(slave)->regs;
 	int ret = 0;
@@ -283,10 +283,10 @@ int spi_xfer(struct spi_slave *slave, const void *dout,
 	 * seems to work fine.
 	 */
 	while (bytes_out || bytes_in) {
-		unsigned int in_now = MIN(bytes_in, 0xfffe);
-		unsigned int out_now = MIN(bytes_out, 0xfffe);
-		unsigned int in_rem, out_rem;
-		unsigned int mask;
+		size_t in_now = MIN(bytes_in, 0xfffe);
+		size_t out_now = MIN(bytes_out, 0xfffe);
+		size_t in_rem, out_rem;
+		size_t mask;
 		bool use_16bit;
 
 		rockchip_spi_enable_chip(regs, 0);
@@ -324,13 +324,13 @@ int spi_xfer(struct spi_slave *slave, const void *dout,
 			break;
 
 		if (bytes_out) {
-			unsigned int sent = out_now - out_rem;
+			size_t sent = out_now - out_rem;
 			bytes_out -= sent;
 			dout += sent;
 		}
 
 		if (bytes_in) {
-			unsigned int received = in_now - in_rem;
+			size_t received = in_now - in_rem;
 			bytes_in -= received;
 			din += received;
 		}
diff --git a/src/soc/samsung/exynos5420/spi.c b/src/soc/samsung/exynos5420/spi.c
index fd31a2fdf7..c2faeb5198 100644
--- a/src/soc/samsung/exynos5420/spi.c
+++ b/src/soc/samsung/exynos5420/spi.c
@@ -58,7 +58,7 @@ static struct exynos_spi_slave exynos_spi_slaves[3] = {
 	},
 };
 
-static inline struct exynos_spi_slave *to_exynos_spi(struct spi_slave *slave)
+static inline struct exynos_spi_slave *to_exynos_spi(const struct spi_slave *slave)
 {
 	return container_of(slave, struct exynos_spi_slave, slave);
 }
@@ -128,7 +128,7 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs)
 	return &eslave->slave;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	struct exynos_spi *regs = to_exynos_spi(slave)->regs;
 	// TODO(hungte) Add some delay if too many transactions happen at once.
@@ -137,19 +137,19 @@ int spi_claim_bus(struct spi_slave *slave)
 }
 
 static void spi_transfer(struct exynos_spi *regs, void *in, const void *out,
-			 u32 size)
+			 size_t size)
 {
 	u8 *inb = in;
 	const u8 *outb = out;
 
-	int width = (size % 4) ? 1 : 4;
+	size_t width = (size % 4) ? 1 : 4;
 
 	while (size) {
-		int packets = size / width;
+		size_t packets = size / width;
 		// The packet count field is 16 bits wide.
 		packets = MIN(packets, (1 << 16) - 1);
 
-		int out_bytes, in_bytes;
+		size_t out_bytes, in_bytes;
 		out_bytes = in_bytes = packets * width;
 
 		spi_sw_reset(regs, width == 4);
@@ -188,13 +188,13 @@ static void spi_transfer(struct exynos_spi *regs, void *in, const void *out,
 	}
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout, unsigned int bytes_out,
-	     void *din, unsigned int bytes_in)
+int spi_xfer(const struct spi_slave *slave, const void *dout, size_t bytes_out,
+	     void *din, size_t bytes_in)
 {
 	struct exynos_spi *regs = to_exynos_spi(slave)->regs;
 
 	if (bytes_out && bytes_in) {
-		u32 min_size = MIN(bytes_out, bytes_in);
+		size_t min_size = MIN(bytes_out, bytes_in);
 
 		spi_transfer(regs, din, dout, min_size);
 
@@ -213,7 +213,7 @@ int spi_xfer(struct spi_slave *slave, const void *dout, unsigned int bytes_out,
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	struct exynos_spi *regs = to_exynos_spi(slave)->regs;
 	setbits_le32(&regs->cs_reg, SPI_SLAVE_SIG_INACT);
diff --git a/src/southbridge/amd/agesa/hudson/spi.c b/src/southbridge/amd/agesa/hudson/spi.c
index f1a82e9022..7bb0e3f124 100644
--- a/src/southbridge/amd/agesa/hudson/spi.c
+++ b/src/southbridge/amd/agesa/hudson/spi.c
@@ -90,13 +90,13 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(AMD_SB_SPI_TX_LEN - cmd_len, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	/* First byte is cmd which can not being sent through FIFO. */
 	u8 cmd = *(u8 *)dout++;
 	u8 readoffby1;
-	u8 count;
+	size_t count;
 
 	bytesout--;
 
@@ -147,13 +147,13 @@ int spi_xfer(struct spi_slave *slave, const void *dout,
 	return 0;
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Nothing is required. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Nothing is required. */
 }
diff --git a/src/southbridge/amd/cimx/sb800/spi.c b/src/southbridge/amd/cimx/sb800/spi.c
index 726d8e0129..2522c2e5b5 100644
--- a/src/southbridge/amd/cimx/sb800/spi.c
+++ b/src/southbridge/amd/cimx/sb800/spi.c
@@ -59,14 +59,14 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(AMD_SB_SPI_TX_LEN - cmd_len, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	/* First byte is cmd which can not being sent through FIFO. */
 	u8 cmd = *(u8 *)dout++;
 	u8 readoffby1;
 	u8 readwrite;
-	u8 count;
+	size_t count;
 
 	bytesout--;
 
@@ -138,13 +138,13 @@ static void ImcWakeup(void)
 	WaitForEcLDN9MailboxCmdAck();
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Nothing is required. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Nothing is required. */
 	return;
diff --git a/src/southbridge/amd/sb700/spi.c b/src/southbridge/amd/sb700/spi.c
index fa316f16e6..2b1ae2dcc8 100644
--- a/src/southbridge/amd/sb700/spi.c
+++ b/src/southbridge/amd/sb700/spi.c
@@ -65,13 +65,13 @@ static void execute_command(void)
 		(read8((void *)(spibar+3)) & 0x80));
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled internally by the SB700 */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled internally by the SB700 */
 }
@@ -89,14 +89,14 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs)
 	return slave;
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	/* First byte is cmd which cannot be sent through the FIFO. */
 	u8 cmd = *(u8 *)dout++;
 	u8 readoffby1;
 	u8 readwrite;
-	u8 count;
+	size_t count;
 
 	uint32_t spibar = get_spi_bar();
 
diff --git a/src/southbridge/amd/sb700/spi.h b/src/southbridge/amd/sb700/spi.h
index ed5b8588fe..605f3eedf2 100644
--- a/src/southbridge/amd/sb700/spi.h
+++ b/src/southbridge/amd/sb700/spi.h
@@ -13,5 +13,5 @@
  * GNU General Public License for more details.
  */
 
-int spi_claim_bus(struct spi_slave *slave);
-void spi_release_bus(struct spi_slave *slave);
+int spi_claim_bus(const struct spi_slave *slave);
+void spi_release_bus(const struct spi_slave *slave);
diff --git a/src/southbridge/intel/common/spi.c b/src/southbridge/intel/common/spi.c
index 36102c201c..2d36d38354 100644
--- a/src/southbridge/intel/common/spi.c
+++ b/src/southbridge/intel/common/spi.c
@@ -357,13 +357,13 @@ static void spi_init_cb(void *unused)
 
 BOOT_STATE_INIT_ENTRY(BS_DEV_INIT, BS_ON_ENTRY, spi_init_cb, NULL);
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 }
@@ -536,8 +536,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(cntlr.databytes, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	uint16_t control;
 	int16_t opcode_index;
diff --git a/src/southbridge/intel/fsp_rangeley/spi.c b/src/southbridge/intel/fsp_rangeley/spi.c
index 8b0c3c1f72..8a0fac2f92 100644
--- a/src/southbridge/intel/fsp_rangeley/spi.c
+++ b/src/southbridge/intel/fsp_rangeley/spi.c
@@ -429,13 +429,13 @@ void spi_init(void)
 	}
 }
 
-int spi_claim_bus(struct spi_slave *slave)
+int spi_claim_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 	return 0;
 }
 
-void spi_release_bus(struct spi_slave *slave)
+void spi_release_bus(const struct spi_slave *slave)
 {
 	/* Handled by ICH automatically. */
 }
@@ -601,8 +601,8 @@ unsigned int spi_crop_chunk(unsigned int cmd_len, unsigned int buf_len)
 	return min(cntlr.databytes, buf_len);
 }
 
-int spi_xfer(struct spi_slave *slave, const void *dout,
-		unsigned int bytesout, void *din, unsigned int bytesin)
+int spi_xfer(const struct spi_slave *slave, const void *dout,
+		size_t bytesout, void *din, size_t bytesin)
 {
 	uint16_t control;
 	int16_t opcode_index;