From 31b66b686ef574df45dc09e84d84e70db32beb17 Mon Sep 17 00:00:00 2001 From: Luke Wren Date: Fri, 21 Aug 2015 23:14:48 +0100 Subject: [PATCH] Add /dev/gpiomem device for rootless user GPIO access Signed-off-by: Luke Wren bcm2835-gpiomem: Fix for ARCH_BCM2835 builds Build on ARCH_BCM2835, and fail to probe if no IO resource. See: https://github.com/raspberrypi/linux/issues/1154 --- drivers/char/broadcom/Kconfig | 8 + drivers/char/broadcom/Makefile | 1 + drivers/char/broadcom/bcm2835-gpiomem.c | 258 ++++++++++++++++++++++++ 3 files changed, 267 insertions(+) create mode 100644 drivers/char/broadcom/bcm2835-gpiomem.c --- a/drivers/char/broadcom/Kconfig +++ b/drivers/char/broadcom/Kconfig @@ -16,3 +16,11 @@ config BCM2708_VCMEM Helper for videocore memory access and total size allocation. endif + +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. --- a/drivers/char/broadcom/Makefile +++ b/drivers/char/broadcom/Makefile @@ -1 +1,2 @@ obj-$(CONFIG_BCM2708_VCMEM) += vc_mem.o +obj-$(CONFIG_BCM2835_DEVGPIOMEM)+= bcm2835-gpiomem.o --- /dev/null +++ b/drivers/char/broadcom/bcm2835-gpiomem.c @@ -0,0 +1,258 @@ +/** + * 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 + * 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 +#include +#include +#include +#include +#include +#include +#include +#include + +#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; + + 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 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; + + ioresource = platform_get_resource(pdev, IORESOURCE_MEM, 0); + if (ioresource) { + inst->gpio_regs_phys = ioresource->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(&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; + + 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: +failed_get_resource: + 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 ");