Add /dev/gpiomem device for rootless user GPIO access

arch/arm/boot/dts/bcm2708.dtsi

@@ -15,5 +15,11 @@
 		arm-pmu {
 			compatible = "arm,arm1176-pmu";
 		};
+
+		gpiomem {
+			compatible = "brcm,bcm2835-gpiomem";
+			reg = <0x7e200000 0x1000>;
+			status = "okay";
+		};
 	};
 };

arch/arm/boot/dts/bcm2709.dtsi

@@ -16,6 +16,12 @@
 			compatible = "arm,cortex-a7-pmu";
 			interrupts = <3 9>;
 		};
+
+		gpiomem {
+			compatible = "brcm,bcm2835-gpiomem";
+			reg = <0x7e200000 0x1000>;
+			status = "okay";
+		};
 	};
 
 	timer {

drivers/char/broadcom/Kconfig

@@ -38,3 +38,12 @@ config BCM_VC_SM
 	help
 	Support for the VC shared memory on the Broadcom reference
 	design. Uses the VCHIQ stack.
+
+config BCM2835_DEVGPIOMEM
+	tristate "/dev/gpiomem rootless GPIO access via mmap() on the BCM2835"
+	default m
+	help
+		Provides users with root-free access to the GPIO registers
+		on the 2835. Calling mmap(/dev/gpiomem) will map the GPIO
+		register page to the user's pointer.
+

drivers/char/broadcom/Makefile

@@ -2,3 +2,6 @@ obj-$(CONFIG_BCM_VC_CMA)	+= vc_cma/
 obj-$(CONFIG_BCM2708_VCMEM)	+= vc_mem.o
 obj-$(CONFIG_BCM_VCIO)		+= vcio.o
 obj-$(CONFIG_BCM_VC_SM)         += vc_sm/
+
+obj-$(CONFIG_BCM2835_DEVGPIOMEM)+= bcm2835-gpiomem.o
+

drivers/char/broadcom/bcm2835-gpiomem.c

@@ -0,0 +1,265 @@
+/**
+ * GPIO memory device driver
+ *
+ * Creates a chardev /dev/gpiomem which will provide user access to
+ * the BCM2835's GPIO registers when it is mmap()'d.
+ * No longer need root for user GPIO access, but without relaxing permissions
+ * on /dev/mem.
+ *
+ * Written by Luke Wren <[email protected]>
+ * 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>
+
+#define DEVICE_NAME "bcm2835-gpiomem"
+#define DRIVER_NAME "gpiomem-bcm2835"
+#define DEVICE_MINOR 0
+
+struct bcm2835_gpiomem_instance {
+	unsigned long gpio_regs_phys;
+	struct device *dev;
+};
+
+static struct cdev bcm2835_gpiomem_cdev;
+static dev_t bcm2835_gpiomem_devid;
+static struct class *bcm2835_gpiomem_class;
+static struct device *bcm2835_gpiomem_dev;
+static struct bcm2835_gpiomem_instance *inst;
+
+
+/****************************************************************************
+*
+*   GPIO mem chardev file ops
+*
+***************************************************************************/
+
+static int bcm2835_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 bcm2835_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 bcm2835_gpiomem_vm_ops = {
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+	.access = generic_access_phys
+#endif
+};
+
+static int bcm2835_gpiomem_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	/* Ignore what the user says - they're getting the GPIO regs
+	   whether they like it or not! */
+	unsigned long gpio_page = inst->gpio_regs_phys >> PAGE_SHIFT;
+
+	vma->vm_page_prot = phys_mem_access_prot(file, gpio_page,
+						 PAGE_SIZE,
+						 vma->vm_page_prot);
+	vma->vm_ops = &bcm2835_gpiomem_vm_ops;
+	if (remap_pfn_range(vma, vma->vm_start,
+			gpio_page,
+			PAGE_SIZE,
+			vma->vm_page_prot)) {
+		return -EAGAIN;
+	}
+	return 0;
+}
+
+static const struct file_operations
+bcm2835_gpiomem_fops = {
+	.owner = THIS_MODULE,
+	.open = bcm2835_gpiomem_open,
+	.release = bcm2835_gpiomem_release,
+	.mmap = bcm2835_gpiomem_mmap,
+};
+
+
+ /****************************************************************************
+*
+*   Probe and remove functions
+*
+***************************************************************************/
+
+
+static int bcm2835_gpiomem_probe(struct platform_device *pdev)
+{
+	int err;
+	void *ptr_err;
+	struct device *dev = &pdev->dev;
+	struct device_node *node = dev->of_node;
+	struct resource *ioresource;
+
+	/* Allocate buffers and instance data */
+
+	inst = kzalloc(sizeof(struct bcm2835_gpiomem_instance), GFP_KERNEL);
+
+	if (!inst) {
+		err = -ENOMEM;
+		goto failed_inst_alloc;
+	}
+
+	inst->dev = dev;
+
+	/* Create character device entries */
+
+	err = alloc_chrdev_region(&bcm2835_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(&bcm2835_gpiomem_cdev, &bcm2835_gpiomem_fops);
+	bcm2835_gpiomem_cdev.owner = THIS_MODULE;
+	err = cdev_add(&bcm2835_gpiomem_cdev, bcm2835_gpiomem_devid, 1);
+	if (err != 0) {
+		dev_err(inst->dev, "unable to register device");
+		goto failed_cdev_add;
+	}
+
+	/* Create sysfs entries */
+
+	bcm2835_gpiomem_class = class_create(THIS_MODULE, DEVICE_NAME);
+	ptr_err = bcm2835_gpiomem_class;
+	if (IS_ERR(ptr_err))
+		goto failed_class_create;
+
+	bcm2835_gpiomem_dev = device_create(bcm2835_gpiomem_class, NULL,
+					bcm2835_gpiomem_devid, NULL,
+					"gpiomem");
+	ptr_err = bcm2835_gpiomem_dev;
+	if (IS_ERR(ptr_err))
+		goto failed_device_create;
+
+	/* Get address from device tree if available (*_resource() correctly
+	   converts the bus address in device tree to a physical address),
+	   or use hardcoded offset + BCM2708_PERI_BASE if not.
+	   (In spite of its name 2708 actually seems to have the correct
+	   mach-dependent value on 2709 etc, as it is defined in
+	   mach-bcm270x/platform.h) */
+
+	if (node) {
+		ioresource = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+		inst->gpio_regs_phys = ioresource->start;
+	} else {
+		inst->gpio_regs_phys = GPIO_BASE;
+	}
+
+	dev_info(inst->dev, "Initialised: Registers at 0x%08lx",
+		inst->gpio_regs_phys);
+
+	return 0;
+
+failed_device_create:
+	class_destroy(bcm2835_gpiomem_class);
+failed_class_create:
+	cdev_del(&bcm2835_gpiomem_cdev);
+	err = PTR_ERR(ptr_err);
+failed_cdev_add:
+	unregister_chrdev_region(bcm2835_gpiomem_devid, 1);
+failed_alloc_chrdev:
+	kfree(inst);
+failed_inst_alloc:
+	dev_err(inst->dev, "could not load bcm2835_gpiomem");
+	return err;
+}
+
+static int bcm2835_gpiomem_remove(struct platform_device *pdev)
+{
+	struct device *dev = inst->dev;
+
+	kfree(inst);
+	device_destroy(bcm2835_gpiomem_class, bcm2835_gpiomem_devid);
+	class_destroy(bcm2835_gpiomem_class);
+	cdev_del(&bcm2835_gpiomem_cdev);
+	unregister_chrdev_region(bcm2835_gpiomem_devid, 1);
+
+	dev_info(dev, "GPIO mem driver removed - OK");
+	return 0;
+}
+
+ /****************************************************************************
+*
+*   Register the driver with device tree
+*
+***************************************************************************/
+
+static const struct of_device_id bcm2835_gpiomem_of_match[] = {
+	{.compatible = "brcm,bcm2835-gpiomem",},
+	{ /* sentinel */ },
+};
+
+MODULE_DEVICE_TABLE(of, bcm2835_gpiomem_of_match);
+
+static struct platform_driver bcm2835_gpiomem_driver = {
+	.probe = bcm2835_gpiomem_probe,
+	.remove = bcm2835_gpiomem_remove,
+	.driver = {
+		   .name = DRIVER_NAME,
+		   .owner = THIS_MODULE,
+		   .of_match_table = bcm2835_gpiomem_of_match,
+		   },
+};
+
+module_platform_driver(bcm2835_gpiomem_driver);
+
+MODULE_ALIAS("platform:gpiomem-bcm2835");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("gpiomem driver for accessing GPIO from userspace");
+MODULE_AUTHOR("Luke Wren <[email protected]>");