spi-nor: Add support for Intel SPI serial flash controller

Add support for the SPI serial flash host controller found on many Intel
CPUs including Baytrail and Braswell. The SPI serial flash controller is
used to access BIOS and other platform specific information. By default the
driver exposes a single read-only MTD device but with a module parameter
"writeable=1" the MTD device can be made read-write which makes it possible
to upgrade BIOS directly from Linux.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/mtd/intel-spi.txt

+Upgrading BIOS using intel-spi
+------------------------------
+
+Many Intel CPUs like Baytrail and Braswell include SPI serial flash host
+controller which is used to hold BIOS and other platform specific data.
+Since contents of the SPI serial flash is crucial for machine to function,
+it is typically protected by different hardware protection mechanisms to
+avoid accidental (or on purpose) overwrite of the content.
+
+Not all manufacturers protect the SPI serial flash, mainly because it
+allows upgrading the BIOS image directly from an OS.
+
+The intel-spi driver makes it possible to read and write the SPI serial
+flash, if certain protection bits are not set and locked. If it finds
+any of them set, the whole MTD device is made read-only to prevent
+partial overwrites. By default the driver exposes SPI serial flash
+contents as read-only but it can be changed from kernel command line,
+passing "intel-spi.writeable=1".
+
+Please keep in mind that overwriting the BIOS image on SPI serial flash
+might render the machine unbootable and requires special equipment like
+Dediprog to revive. You have been warned!
+
+Below are the steps how to upgrade MinnowBoard MAX BIOS directly from
+Linux.
+
+ 1) Download and extract the latest Minnowboard MAX BIOS SPI image
+    [1]. At the time writing this the latest image is v92.
+
+ 2) Install mtd-utils package [2]. We need this in order to erase the SPI
+    serial flash. Distros like Debian and Fedora have this prepackaged with
+    name "mtd-utils".
+
+ 3) Add "intel-spi.writeable=1" to the kernel command line and reboot
+    the board (you can also reload the driver passing "writeable=1" as
+    module parameter to modprobe).
+
+ 4) Once the board is up and running again, find the right MTD partition
+    (it is named as "BIOS"):
+
+    # cat /proc/mtd
+    dev:    size   erasesize  name
+    mtd0: 00800000 00001000 "BIOS"
+
+    So here it will be /dev/mtd0 but it may vary.
+
+ 5) Make backup of the existing image first:
+
+    # dd if=/dev/mtd0ro of=bios.bak
+    16384+0 records in
+    16384+0 records out
+    8388608 bytes (8.4 MB) copied, 10.0269 s, 837 kB/s
+
+ 6) Verify the backup
+
+    # sha1sum /dev/mtd0ro bios.bak
+    fdbb011920572ca6c991377c4b418a0502668b73  /dev/mtd0ro
+    fdbb011920572ca6c991377c4b418a0502668b73  bios.bak
+
+    The SHA1 sums must match. Otherwise do not continue any further!
+
+ 7) Erase the SPI serial flash. After this step, do not reboot the
+    board! Otherwise it will not start anymore.
+
+    # flash_erase /dev/mtd0 0 0
+    Erasing 4 Kibyte @ 7ff000 -- 100 % complete
+
+ 8) Once completed without errors you can write the new BIOS image:
+
+    # dd if=MNW2MAX1.X64.0092.R01.1605221712.bin of=/dev/mtd0
+
+ 9) Verify that the new content of the SPI serial flash matches the new
+    BIOS image:
+
+    # sha1sum /dev/mtd0ro MNW2MAX1.X64.0092.R01.1605221712.bin
+    9b4df9e4be2057fceec3a5529ec3d950836c87a2  /dev/mtd0ro
+    9b4df9e4be2057fceec3a5529ec3d950836c87a2 MNW2MAX1.X64.0092.R01.1605221712.bin
+
+    The SHA1 sums should match.
+
+ 10) Now you can reboot your board and observe the new BIOS starting up
+     properly.
+
+References
+----------
+
+[1] https://firmware.intel.com/sites/default/files/MinnowBoard.MAX_.X64.92.R01.zip
+[2] http://www.linux-mtd.infradead.org/

drivers/mtd/spi-nor/Kconfig

@@ -76,4 +76,24 @@ config SPI_NXP_SPIFI
 	  Flash. Enable this option if you have a device with a SPIFI
 	  controller and want to access the Flash as a mtd device.
 
+config SPI_INTEL_SPI
+	tristate
+
+config SPI_INTEL_SPI_PLATFORM
+	tristate "Intel PCH/PCU SPI flash platform driver" if EXPERT
+	depends on X86
+	select SPI_INTEL_SPI
+	help
+	  This enables platform support for the Intel PCH/PCU SPI
+	  controller in master mode. This controller is present in modern
+	  Intel hardware and is used to hold BIOS and other persistent
+	  settings. Using this driver it is possible to upgrade BIOS
+	  directly from Linux.
+
+	  Say N here unless you know what you are doing. Overwriting the
+	  SPI flash may render the system unbootable.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called intel-spi-platform.
+
 endif # MTD_SPI_NOR

drivers/mtd/spi-nor/Makefile

@@ -5,3 +5,5 @@ obj-$(CONFIG_SPI_FSL_QUADSPI)	+= fsl-quadspi.o
 obj-$(CONFIG_SPI_HISI_SFC)	+= hisi-sfc.o
 obj-$(CONFIG_MTD_MT81xx_NOR)    += mtk-quadspi.o
 obj-$(CONFIG_SPI_NXP_SPIFI)	+= nxp-spifi.o
+obj-$(CONFIG_SPI_INTEL_SPI)	+= intel-spi.o
+obj-$(CONFIG_SPI_INTEL_SPI_PLATFORM)	+= intel-spi-platform.o

drivers/mtd/spi-nor/intel-spi-platform.c

+/*
+ * Intel PCH/PCU SPI flash platform driver.
+ *
+ * Copyright (C) 2016, Intel Corporation
+ * Author: Mika Westerberg <mika.westerberg@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/ioport.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include "intel-spi.h"
+
+static int intel_spi_platform_probe(struct platform_device *pdev)
+{
+	struct intel_spi_boardinfo *info;
+	struct intel_spi *ispi;
+	struct resource *mem;
+
+	info = dev_get_platdata(&pdev->dev);
+	if (!info)
+		return -EINVAL;
+
+	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	ispi = intel_spi_probe(&pdev->dev, mem, info);
+	if (IS_ERR(ispi))
+		return PTR_ERR(ispi);
+
+	platform_set_drvdata(pdev, ispi);
+	return 0;
+}
+
+static int intel_spi_platform_remove(struct platform_device *pdev)
+{
+	struct intel_spi *ispi = platform_get_drvdata(pdev);
+
+	return intel_spi_remove(ispi);
+}
+
+static struct platform_driver intel_spi_platform_driver = {
+	.probe = intel_spi_platform_probe,
+	.remove = intel_spi_platform_remove,
+	.driver = {
+		.name = "intel-spi",
+	},
+};
+
+module_platform_driver(intel_spi_platform_driver);
+
+MODULE_DESCRIPTION("Intel PCH/PCU SPI flash platform driver");
+MODULE_AUTHOR("Mika Westerberg <mika.westerberg@linux.intel.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:intel-spi");

drivers/mtd/spi-nor/intel-spi.h

+/*
+ * Intel PCH/PCU SPI flash driver.
+ *
+ * Copyright (C) 2016, Intel Corporation
+ * Author: Mika Westerberg <mika.westerberg@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef INTEL_SPI_H
+#define INTEL_SPI_H
+
+#include <linux/platform_data/intel-spi.h>
+
+struct intel_spi;
+struct resource;
+
+struct intel_spi *intel_spi_probe(struct device *dev,
+	struct resource *mem, const struct intel_spi_boardinfo *info);
+int intel_spi_remove(struct intel_spi *ispi);
+
+#endif /* INTEL_SPI_H */

include/linux/platform_data/intel-spi.h

+/*
+ * Intel PCH/PCU SPI flash driver.
+ *
+ * Copyright (C) 2016, Intel Corporation
+ * Author: Mika Westerberg <mika.westerberg@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef INTEL_SPI_PDATA_H
+#define INTEL_SPI_PDATA_H
+
+enum intel_spi_type {
+	INTEL_SPI_BYT = 1,
+	INTEL_SPI_LPT,
+	INTEL_SPI_BXT,
+};
+
+/**
+ * struct intel_spi_boardinfo - Board specific data for Intel SPI driver
+ * @type: Type which this controller is compatible with
+ * @writeable: The chip is writeable
+ */
+struct intel_spi_boardinfo {
+	enum intel_spi_type type;
+	bool writeable;
+};
+
+#endif /* INTEL_SPI_PDATA_H */