device/i2c_bus: Add i2c_dev_read_at16()

i2c_dev_read_at16() sends a 16-bit offset to the I2C chip (for larger
EEPROM parts), then reads bytes up to a given length into a buffer.

Change-Id: I7516f3e5d9aca362c2b340aa5627d91510c09412
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/29478
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/device/i2c_bus.c

@@ -16,6 +16,7 @@
 #include <console/console.h>
 #include <device/smbus.h>
 #include <device/i2c_bus.h>
+#include <commonlib/endian.h>
 
 struct bus *i2c_link(struct device *const dev)
 {
@@ -159,3 +160,39 @@ int i2c_dev_writeb_at(struct device *const dev,
 		return -1;
 	}
 }
+
+int i2c_dev_read_at16(struct device *const dev,
+		      uint8_t *const buf, const size_t len, uint16_t off)
+{
+	struct device *const busdev = i2c_busdev(dev);
+	if (!busdev)
+		return -1;
+
+	if (busdev->ops->ops_i2c_bus) {
+		const struct i2c_msg msg[] = {
+			{
+				.flags	= 0,
+				.slave	= dev->path.i2c.device,
+				.buf	= (uint8_t *)&off,
+				.len	= sizeof(off),
+			},
+			{
+				.flags	= I2C_M_RD,
+				.slave	= dev->path.i2c.device,
+				.buf	= buf,
+				.len	= len,
+			},
+		};
+
+		write_be16(&off, off);
+		const int ret = busdev->ops->ops_i2c_bus->transfer(
+					busdev, msg, ARRAY_SIZE(msg));
+		if (ret)
+			return ret;
+		else
+			return len;
+	} else {
+		printk(BIOS_ERR, "%s Missing ops_i2c_bus->transfer", dev_path(busdev));
+		return -1;
+	}
+}

src/include/device/i2c_bus.h

@@ -89,4 +89,12 @@ int i2c_dev_readb_at(struct device *, uint8_t off);
  */
 int i2c_dev_writeb_at(struct device *, uint8_t off, uint8_t val);
 
+/*
+ * Sends the 16-bit register offset `off` and reads `len` bytes into `buf`.
+ *
+ * Returns the number of bytes read on success, negative `enum cb_err`
+ * value on error.
+ */
+int i2c_dev_read_at16(struct device *, uint8_t *buf, size_t len, uint16_t off);
+
 #endif	/* _DEVICE_I2C_BUS_H_ */