char: exynos: add /dev/gpiomem device for rootless user GPIO access

Change-Id: Ic734a87999d1ef433af500560dada9eb2a69cb08

arch/arm/boot/dts/exynos5422-odroidxu3-common.dtsi

@@ -44,6 +44,13 @@
 		};
 	};
 
+	gpiomem {
+		compatible = "samsung,exynos-gpiomem";
+		reg = <0x13400000 0x1000>,
+		      <0x14010000 0x1000>;
+		status = "okay";
+	};
+
 	emmc_pwrseq: pwrseq {
 		pinctrl-0 = <&emmc_nrst_pin>;
 		pinctrl-names = "default";

drivers/char/Kconfig

@@ -590,5 +590,14 @@ config TILE_SROM
 
 source "drivers/char/xillybus/Kconfig"
 
+config EXYNOS_GPIOMEM
+	tristate "/dev/gpiomem rootless GPIO access via mmap() on the EXYNOS"
+	default m
+	---help---
+	  Provides users with root-free access to the GPIO registers
+	  on EXYNOS. Calling mmap(/dev/gpiomem) will map the GPIO register
+	  page to the user's pointer. This drvier can allow to access gpio
+	  memory area in user account.
+
 endmenu
 

drivers/char/Makefile

@@ -60,3 +60,4 @@ js-rtc-y = rtc.o
 obj-$(CONFIG_TILE_SROM)		+= tile-srom.o
 obj-$(CONFIG_XILLYBUS)		+= xillybus/
 obj-$(CONFIG_POWERNV_OP_PANEL)	+= powernv-op-panel.o
+obj-$(CONFIG_EXYNOS_GPIOMEM)	+= exynos-gpiomem.o

drivers/char/exynos-gpiomem.c

@@ -0,0 +1,270 @@
+/*
+ * linux/drivers/char/exynos-gpiomem.c
+ *
+ * GPIO memory device driver
+ *
+ * Creates a chardev /dev/gpiomem which will provide user access to
+ * the EXYNOS's GPIO registers when it is mmap()'d.
+ * No longer need root for user GPIO access, but without relaxing permissions
+ * on /dev/mem.
+ *
+ * Copyright (c) 2017 Hardkernel Co., Ltd.
+ *
+ * This driver is based on bcm2835-gpiomem.c in Raspberrypi's linux kernel 4.4:
+ *	Written by Luke Wren <luke@raspberrypi.org>
+ *	Copyright (c) 2015, Raspberry Pi (Trading) Ltd.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions, and the following disclaimer,
+ *    without modification.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The names of the above-listed copyright holders may not be used
+ *    to endorse or promote products derived from this software without
+ *    specific prior written permission.
+ *
+ * ALTERNATIVELY, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2, as published by the Free
+ * Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/cdev.h>
+#include <linux/pagemap.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <asm/io.h>
+
+#define DEVICE_NAME "exynos-gpiomem"
+#define DRIVER_NAME "gpiomem-exynos"
+#define DEVICE_MINOR 0
+
+struct exynos_gpiomem_instance {
+	unsigned long gpio_regs_phys[32];
+	int gpio_area_count;
+	struct device *dev;
+};
+
+static struct cdev exynos_gpiomem_cdev;
+static dev_t exynos_gpiomem_devid;
+static struct class *exynos_gpiomem_class;
+static struct device *exynos_gpiomem_dev;
+static struct exynos_gpiomem_instance *inst;
+
+static int exynos_gpiomem_open(struct inode *inode, struct file *file)
+{
+	int dev = iminor(inode);
+	int ret = 0;
+
+	dev_info(inst->dev, "gpiomem device opened.");
+
+	if (dev != DEVICE_MINOR) {
+		dev_err(inst->dev, "Unknown minor device: %d", dev);
+		ret = -ENXIO;
+	}
+	return ret;
+}
+
+static int exynos_gpiomem_release(struct inode *inode, struct file *file)
+{
+	int dev = iminor(inode);
+	int ret = 0;
+
+	if (dev != DEVICE_MINOR) {
+		dev_err(inst->dev, "Unknown minor device %d", dev);
+		ret = -ENXIO;
+	}
+	return ret;
+}
+
+static const struct vm_operations_struct exynos_gpiomem_vm_ops = {
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+	.access = generic_access_phys
+#endif
+};
+
+static int exynos_gpiomem_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	int gpio_area = 0;
+
+	while (gpio_area < inst->gpio_area_count) {
+		if ((inst->gpio_regs_phys[gpio_area] >> PAGE_SHIFT) == vma->vm_pgoff)
+			goto found;
+
+		gpio_area++;
+	}
+
+	return -EACCES;
+
+found:
+	vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
+			PAGE_SIZE,
+			vma->vm_page_prot);
+
+	vma->vm_ops = &exynos_gpiomem_vm_ops;
+
+	if (remap_pfn_range(vma, vma->vm_start,
+				vma->vm_pgoff,
+				PAGE_SIZE,
+				vma->vm_page_prot)) {
+		return -EAGAIN;
+	}
+
+	return 0;
+}
+
+static const struct file_operations
+exynos_gpiomem_fops = {
+	.owner = THIS_MODULE,
+	.open = exynos_gpiomem_open,
+	.release = exynos_gpiomem_release,
+	.mmap = exynos_gpiomem_mmap,
+};
+
+static int exynos_gpiomem_probe(struct platform_device *pdev)
+{
+	int err = 0;
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct resource *res = NULL;
+	int i = 0;
+
+	/* Allocate buffers and instance data */
+	inst = kzalloc(sizeof(struct exynos_gpiomem_instance), GFP_KERNEL);
+
+	if (!inst) {
+		err = -ENOMEM;
+		goto failed_inst_alloc;
+	}
+
+	inst->dev = dev;
+
+	inst->gpio_area_count = of_property_count_elems_of_size(np, "reg",
+				sizeof(u32)) / 2;
+
+	if (inst->gpio_area_count > 32 || inst->gpio_area_count <= 0) {
+		dev_err(inst->dev, "failed to get gpio register area.");
+		err = -EINVAL;
+		goto failed_inst_alloc;
+	}
+
+	dev_info(inst->dev, "Initialised: GPIO register area is %d",
+			inst->gpio_area_count);
+
+	for (i = 0; i < inst->gpio_area_count; ++i) {
+		res = platform_get_resource(pdev, IORESOURCE_MEM, i);
+		if (res) {
+			inst->gpio_regs_phys[i] = res->start;
+		} else {
+			dev_err(inst->dev, "failed to get IO resource");
+			err = -ENOENT;
+			goto failed_get_resource;
+		}
+	}
+
+	/* Create character device entries */
+	err = alloc_chrdev_region(&exynos_gpiomem_devid,
+				  DEVICE_MINOR, 1, DEVICE_NAME);
+	if (err != 0) {
+		dev_err(inst->dev, "unable to allocate device number");
+		goto failed_alloc_chrdev;
+	}
+	cdev_init(&exynos_gpiomem_cdev, &exynos_gpiomem_fops);
+	exynos_gpiomem_cdev.owner = THIS_MODULE;
+	err = cdev_add(&exynos_gpiomem_cdev, exynos_gpiomem_devid, 1);
+	if (err != 0) {
+		dev_err(inst->dev, "unable to register device");
+		goto failed_cdev_add;
+	}
+
+	/* Create sysfs entries */
+	exynos_gpiomem_class = class_create(THIS_MODULE, DEVICE_NAME);
+	err = IS_ERR(exynos_gpiomem_class);
+	if (err)
+		goto failed_class_create;
+
+	exynos_gpiomem_dev = device_create(exynos_gpiomem_class, NULL,
+					exynos_gpiomem_devid, NULL,
+					"gpiomem");
+	err = IS_ERR(exynos_gpiomem_dev);
+	if (err)
+		goto failed_device_create;
+
+	for (i = 0; i < inst->gpio_area_count; ++i) {
+		dev_info(inst->dev, "Initialised: Registers at 0x%08lx",
+				inst->gpio_regs_phys[i]);
+	}
+
+	return 0;
+
+failed_device_create:
+	class_destroy(exynos_gpiomem_class);
+failed_class_create:
+	cdev_del(&exynos_gpiomem_cdev);
+failed_cdev_add:
+	unregister_chrdev_region(exynos_gpiomem_devid, 1);
+failed_alloc_chrdev:
+failed_get_resource:
+	kfree(inst);
+failed_inst_alloc:
+	dev_err(inst->dev, "could not load exynos_gpiomem");
+	return err;
+}
+
+static int exynos_gpiomem_remove(struct platform_device *pdev)
+{
+	struct device *dev = inst->dev;
+
+	kfree(inst);
+	device_destroy(exynos_gpiomem_class, exynos_gpiomem_devid);
+	class_destroy(exynos_gpiomem_class);
+	cdev_del(&exynos_gpiomem_cdev);
+	unregister_chrdev_region(exynos_gpiomem_devid, 1);
+
+	dev_info(dev, "GPIO mem driver removed - OK");
+	return 0;
+}
+
+static const struct of_device_id exynos_gpiomem_of_match[] = {
+	{.compatible = "samsung,exynos-gpiomem",},
+	{ },
+};
+MODULE_DEVICE_TABLE(of, exynos_gpiomem_of_match);
+
+static struct platform_driver exynos_gpiomem_driver = {
+	.driver			= {
+		.name		= DRIVER_NAME,
+		.owner		= THIS_MODULE,
+		.of_match_table	= exynos_gpiomem_of_match,
+	},
+	.probe			= exynos_gpiomem_probe,
+	.remove			= exynos_gpiomem_remove,
+};
+
+module_platform_driver(exynos_gpiomem_driver);
+
+MODULE_ALIAS("platform:gpiomem-exynos");
+MODULE_DESCRIPTION("EXYNOS gpiomem driver for accessing GPIO from userspace");
+MODULE_AUTHOR("Brian Kim <brian.kim@hardkernel.com>");
+MODULE_LICENSE("GPL");