soc/intel/skylake: Fix SPI WP disable status check

Use SPI write protect disable bit from BIOS_CONTROL register
to check write protect status.

Change-Id: Ie79fb4e3e92a4ae777c5d501abbb44a732a9862a
Signed-off-by: Ravi Sarawadi <ravishankar.sarawadi@intel.com>
Reviewed-on: https://review.coreboot.org/21449
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/common/block/fast_spi/fast_spi.c

@@ -274,3 +274,21 @@ void fast_spi_early_init(uintptr_t spi_base_address)
 	/* Initialize SPI to allow BIOS to write/erase on flash. */
 	fast_spi_init();
 }
+
+/* Read SPI Write Protect disable status. */
+bool fast_spi_wpd_status(void)
+{
+	return pci_read_config16(PCH_DEV_SPI, SPIBAR_BIOS_CONTROL) &
+		SPIBAR_BIOS_CONTROL_WPD;
+}
+
+/* Enable SPI Write Protect. */
+void fast_spi_enable_wp(void)
+{
+	device_t dev = PCH_DEV_SPI;
+	uint8_t bios_cntl;
+
+	bios_cntl = pci_read_config8(dev, SPIBAR_BIOS_CONTROL);
+	bios_cntl &= ~SPIBAR_BIOS_CONTROL_WPD;
+	pci_write_config8(dev, SPIBAR_BIOS_CONTROL, bios_cntl);
+}

src/soc/intel/common/block/include/intelblocks/fast_spi.h

@@ -74,11 +74,18 @@ void fast_spi_cache_bios_region(void);
  * Caching.
  */
 void fast_spi_early_init(uintptr_t spi_base_address);
-
 /*
  * Fast SPI flash controller structure to allow SoCs to define bus-controller
  * mapping.
  */
 extern const struct spi_ctrlr fast_spi_flash_ctrlr;
+/*
+ * Read SPI Write protect disable bit.
+ */
+bool fast_spi_wpd_status(void);
+/*
+ * Enable SPI Write protect.
+ */
+void fast_spi_enable_wp(void);
 
 #endif	/* SOC_INTEL_COMMON_BLOCK_FAST_SPI_H */

src/soc/intel/skylake/smihandler.c

@@ -31,7 +31,6 @@
 #include <pc80/mc146818rtc.h>
 #include <spi-generic.h>
 #include <soc/iomap.h>
-#include <soc/lpc.h>
 #include <soc/nvs.h>
 #include <soc/pci_devs.h>
 #include <soc/pch.h>
@@ -403,23 +402,22 @@ static void southbridge_smi_tco(void)
 		return;
 
 	if (tco_sts & (1 << 8)) { /* BIOSWR */
-		u8 bios_cntl = pci_read_config16(PCH_DEV_SPI, BIOS_CNTL);
-
-		if (bios_cntl & 1) {
-			/*
-			 * BWE is RW, so the SMI was caused by a
-			 * write to BWE, not by a write to the BIOS
-			 *
-			 * This is the place where we notice someone
-			 * is trying to tinker with the BIOS. We are
-			 * trying to be nice and just ignore it. A more
-			 * resolute answer would be to power down the
-			 * box.
-			 */
-			printk(BIOS_DEBUG, "Switching back to RO\n");
-			pci_write_config32(PCH_DEV_SPI, BIOS_CNTL,
-					   (bios_cntl & ~1));
-		} /* No else for now? */
+		if (IS_ENABLED(CONFIG_SPI_FLASH_SMM)) {
+			if (fast_spi_wpd_status()) {
+				/*
+				 * BWE is RW, so the SMI was caused by a
+				 * write to BWE, not by a write to the BIOS
+				 *
+				 * This is the place where we notice someone
+				 * is trying to tinker with the BIOS. We are
+				 * trying to be nice and just ignore it. A more
+				 * resolute answer would be to power down the
+				 * box.
+				 */
+				printk(BIOS_DEBUG, "Switching back to RO\n");
+				fast_spi_enable_wp();
+			} /* No else for now? */
+		}
 	} else if (tco_sts & (1 << 3)) { /* TIMEOUT */
 		/* Handle TCO timeout */
 		printk(BIOS_DEBUG, "TCO Timeout.\n");