ARM: sunxi: Initial support for Allwinner's Security ID fuses

Allwinner has electric fuses (efuse) on their line of chips. This driver
reads those fuses, seeds the kernel entropy and exports them as a sysfs
node.

These fuses are most likely to be programmed at the factory, encoding
things like Chip ID, some sort of serial number, etc. and appear to be
reasonably unique.
While in theory, these should be writeable by the user, it will probably
be inconvenient to do so. Allwinner recommends that a certain input pin,
labeled 'efuse_vddq', be connected to GND. To write these fuses however,
a 2.5 V programming voltage needs to be applied to this pin.

Even so, they can still be used to generate a board-unique mac from,
board unique RSA key and seed the kernel RNG.

On sun7i additional storage is available, this is initially used for an
UEFI BOOT key, Secure JTAG key, HDMI-HDCP key and vendor specific keys.

Currently supported are the following known chips:
Allwinner sun4i (A10)
Allwinner sun5i (A10s, A13)
Allwinner sun7i (A20)

Signed-off-by: Oliver Schinagl <oliver@schinagl.nl>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-driver-sunxi-sid

@@ -0,0 +1,22 @@
+What:		/sys/devices/*/<our-device>/eeprom
+Date:		August 2013
+Contact:	Oliver Schinagl <oliver@schinagl.nl>
+Description:	read-only access to the SID (Security-ID) on current
+		A-series SoC's from Allwinner. Currently supports A10, A10s, A13
+		and A20 CPU's. The earlier A1x series of SoCs exports 16 bytes,
+		whereas the newer A20 SoC exposes 512 bytes split into sections.
+		Besides the 16 bytes of SID, there's also an SJTAG area,
+		HDMI-HDCP key and some custom keys. Below a quick overview, for
+		details see the user manual:
+		0x000  128 bit root-key (sun[457]i)
+		0x010  128 bit boot-key (sun7i)
+		0x020   64 bit security-jtag-key (sun7i)
+		0x028   16 bit key configuration (sun7i)
+		0x02b   16 bit custom-vendor-key (sun7i)
+		0x02c  320 bit low general key (sun7i)
+		0x040   32 bit read-control access (sun7i)
+		0x064  224 bit low general key (sun7i)
+		0x080 2304 bit HDCP-key (sun7i)
+		0x1a0  768 bit high general key (sun7i)
+Users:		any user space application which wants to read the SID on
+		Allwinner's A-series of CPU's.

Documentation/devicetree/bindings/misc/allwinner,sunxi-sid.txt

@@ -0,0 +1,17 @@
+Allwinner sunxi-sid
+
+Required properties:
+- compatible: "allwinner,sun4i-sid" or "allwinner,sun7i-a20-sid".
+- reg: Should contain registers location and length
+
+Example for sun4i:
+	sid@01c23800 {
+		compatible = "allwinner,sun4i-sid";
+		reg = <0x01c23800 0x10>
+	};
+
+Example for sun7i:
+	sid@01c23800 {
+		compatible = "allwinner,sun7i-a20-sid";
+		reg = <0x01c23800 0x200>
+	};

drivers/misc/eeprom/Kconfig

@@ -96,4 +96,17 @@ config EEPROM_DIGSY_MTC_CFG
 
 	  If unsure, say N.
 
+config EEPROM_SUNXI_SID
+	tristate "Allwinner sunxi security ID support"
+	depends on ARCH_SUNXI && SYSFS
+	help
+	  This is a driver for the 'security ID' available on various Allwinner
+	  devices.
+
+	  Due to the potential risks involved with changing e-fuses,
+	  this driver is read-only.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called sunxi_sid.
+
 endmenu

drivers/misc/eeprom/Makefile

@@ -4,4 +4,5 @@ obj-$(CONFIG_EEPROM_LEGACY)	+= eeprom.o
 obj-$(CONFIG_EEPROM_MAX6875)	+= max6875.o
 obj-$(CONFIG_EEPROM_93CX6)	+= eeprom_93cx6.o
 obj-$(CONFIG_EEPROM_93XX46)	+= eeprom_93xx46.o
+obj-$(CONFIG_EEPROM_SUNXI_SID)	+= sunxi_sid.o
 obj-$(CONFIG_EEPROM_DIGSY_MTC_CFG) += digsy_mtc_eeprom.o

drivers/misc/eeprom/sunxi_sid.c

@@ -0,0 +1,158 @@
+/*
+ * Copyright (c) 2013 Oliver Schinagl <oliver@schinagl.nl>
+ * http://www.linux-sunxi.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * This driver exposes the Allwinner security ID, efuses exported in byte-
+ * sized chunks.
+ */
+
+#include <linux/compiler.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/stat.h>
+#include <linux/sysfs.h>
+#include <linux/types.h>
+
+#define DRV_NAME "sunxi-sid"
+
+struct sunxi_sid_data {
+	void __iomem *reg_base;
+	unsigned int keysize;
+};
+
+/* We read the entire key, due to a 32 bit read alignment requirement. Since we
+ * want to return the requested byte, this results in somewhat slower code and
+ * uses 4 times more reads as needed but keeps code simpler. Since the SID is
+ * only very rarely probed, this is not really an issue.
+ */
+static u8 sunxi_sid_read_byte(const struct sunxi_sid_data *sid_data,
+			      const unsigned int offset)
+{
+	u32 sid_key;
+
+	if (offset >= sid_data->keysize)
+		return 0;
+
+	sid_key = ioread32be(sid_data->reg_base + round_down(offset, 4));
+	sid_key >>= (offset % 4) * 8;
+
+	return sid_key; /* Only return the last byte */
+}
+
+static ssize_t sid_read(struct file *fd, struct kobject *kobj,
+			struct bin_attribute *attr, char *buf,
+			loff_t pos, size_t size)
+{
+	struct platform_device *pdev;
+	struct sunxi_sid_data *sid_data;
+	int i;
+
+	pdev = to_platform_device(kobj_to_dev(kobj));
+	sid_data = platform_get_drvdata(pdev);
+
+	if (pos < 0 || pos >= sid_data->keysize)
+		return 0;
+	if (size > sid_data->keysize - pos)
+		size = sid_data->keysize - pos;
+
+	for (i = 0; i < size; i++)
+		buf[i] = sunxi_sid_read_byte(sid_data, pos + i);
+
+	return i;
+}
+
+static struct bin_attribute sid_bin_attr = {
+	.attr = { .name = "eeprom", .mode = S_IRUGO, },
+	.read = sid_read,
+};
+
+static int sunxi_sid_remove(struct platform_device *pdev)
+{
+	device_remove_bin_file(&pdev->dev, &sid_bin_attr);
+	dev_dbg(&pdev->dev, "driver unloaded\n");
+
+	return 0;
+}
+
+static const struct of_device_id sunxi_sid_of_match[] = {
+	{ .compatible = "allwinner,sun4i-sid", .data = (void *)16},
+	{ .compatible = "allwinner,sun7i-a20-sid", .data = (void *)512},
+	{/* sentinel */},
+};
+MODULE_DEVICE_TABLE(of, sunxi_sid_of_match);
+
+static int sunxi_sid_probe(struct platform_device *pdev)
+{
+	struct sunxi_sid_data *sid_data;
+	struct resource *res;
+	const struct of_device_id *of_dev_id;
+	u8 *entropy;
+	unsigned int i;
+
+	sid_data = devm_kzalloc(&pdev->dev, sizeof(struct sunxi_sid_data),
+				GFP_KERNEL);
+	if (!sid_data)
+		return -ENOMEM;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	sid_data->reg_base = devm_ioremap_resource(&pdev->dev, res);
+	if (IS_ERR(sid_data->reg_base))
+		return PTR_ERR(sid_data->reg_base);
+
+	of_dev_id = of_match_device(sunxi_sid_of_match, &pdev->dev);
+	if (!of_dev_id)
+		return -ENODEV;
+	sid_data->keysize = (int)of_dev_id->data;
+
+	platform_set_drvdata(pdev, sid_data);
+
+	sid_bin_attr.size = sid_data->keysize;
+	if (device_create_bin_file(&pdev->dev, &sid_bin_attr))
+		return -ENODEV;
+
+	entropy = kzalloc(sizeof(u8) * sid_data->keysize, GFP_KERNEL);
+	for (i = 0; i < sid_data->keysize; i++)
+		entropy[i] = sunxi_sid_read_byte(sid_data, i);
+	add_device_randomness(entropy, sid_data->keysize);
+	kfree(entropy);
+
+	dev_dbg(&pdev->dev, "loaded\n");
+
+	return 0;
+}
+
+static struct platform_driver sunxi_sid_driver = {
+	.probe = sunxi_sid_probe,
+	.remove = sunxi_sid_remove,
+	.driver = {
+		.name = DRV_NAME,
+		.owner = THIS_MODULE,
+		.of_match_table = sunxi_sid_of_match,
+	},
+};
+module_platform_driver(sunxi_sid_driver);
+
+MODULE_AUTHOR("Oliver Schinagl <oliver@schinagl.nl>");
+MODULE_DESCRIPTION("Allwinner sunxi security id driver");
+MODULE_LICENSE("GPL");