drivers: char: add generic gpiomem driver

Based on bcm2835-gpiomem.

We allow export of the "GPIO registers" to userspace via a chardev as
this allows for finer access control (e.g. users must be group gpio, root
not required).

This driver allows access to either rp1-gpiomem or gpiomem, depending on
which nodes are populated in devicetree.

RP1 has a different look-and-feel to BCM283x SoCs as it has split ranges
for IO controls and the parallel registered OE/IN/OUT access. To handle
this, the driver concatenates the ranges for an IO bank and the
corresponding RIO instance into a contiguous buffer.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>

drivers/char/Kconfig

@@ -424,4 +424,12 @@ config ADI
  and SSM (Silicon Secured Memory). Intended consumers of this
  driver include crash and makedumpfile.
 
+config RASPBERRYPI_GPIOMEM
+ tristate "Rootless GPIO access via mmap() on Raspberry Pi boards"
+ default n
+ help
+ Provides users with root-free access to the GPIO registers
+ on the board. Calling mmap(/dev/gpiomem) will map the GPIO
+ register page to the user's pointer.
+
 endmenu

drivers/char/Makefile

@@ -44,3 +44,4 @@ obj-$(CONFIG_XILLYBUS_CLASS) += xillybus/
 obj-$(CONFIG_POWERNV_OP_PANEL) += powernv-op-panel.o
 obj-$(CONFIG_ADI) += adi.o
 obj-$(CONFIG_BRCM_CHAR_DRIVERS) += broadcom/
+obj-$(CONFIG_RASPBERRYPI_GPIOMEM) += raspberrypi-gpiomem.o

drivers/char/raspberrypi-gpiomem.c

@@ -0,0 +1,275 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+/**
+ * raspberrypi-gpiomem.c
+ *
+ * Provides MMIO access to discontiguous section of Device memory as a linear
+ * user mapping. Successor to bcm2835-gpiomem.c.
+ *
+ * Copyright (c) 2023, Raspberry Pi Ltd.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.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 DRIVER_NAME "rpi-gpiomem"
+#define DEVICE_MINOR 0
+
+/*
+ * Sensible max for a hypothetical "gpio" controller that splits pads,
+ * IO controls, GPIO in/out/enable, and function selection into different
+ * ranges. Most use only one or two.
+ */
+#define MAX_RANGES 4
+
+struct io_windows {
+ unsigned long phys_base;
+ unsigned long len;
+};
+
+struct rpi_gpiomem_priv {
+ dev_t devid;
+ struct class *class;
+ struct cdev rpi_gpiomem_cdev;
+ struct device *dev;
+ const char *name;
+ unsigned int nr_wins;
+ struct io_windows iowins[4];
+};
+
+static int rpi_gpiomem_open(struct inode *inode, struct file *file)
+{
+ int dev = iminor(inode);
+ int ret = 0;
+ struct rpi_gpiomem_priv *priv;
+
+ if (dev != DEVICE_MINOR)
+ ret = -ENXIO;
+
+ priv = container_of(inode->i_cdev, struct rpi_gpiomem_priv,
+ rpi_gpiomem_cdev);
+ if (!priv)
+ return -EINVAL;
+ file->private_data = priv;
+ return ret;
+}
+
+static int rpi_gpiomem_release(struct inode *inode, struct file *file)
+{
+ int dev = iminor(inode);
+ int ret = 0;
+
+ if (dev != DEVICE_MINOR)
+ ret = -ENXIO;
+
+ return ret;
+}
+
+static const struct vm_operations_struct rpi_gpiomem_vm_ops = {
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+ .access = generic_access_phys
+#endif
+};
+
+static int rpi_gpiomem_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ int i;
+ struct rpi_gpiomem_priv *priv;
+ unsigned long base;
+ unsigned long len = 0;
+ unsigned long offset;
+
+ priv = file->private_data;
+ /*
+ * Userspace must provide a virtual address space at least
+ * the size of the concatenated ranges.
+ */
+ for (i = 0; i < priv->nr_wins; i++)
+ len += priv->iowins[i].len;
+ if (len > vma->vm_end - vma->vm_start + 1)
+ return -EINVAL;
+
+ vma->vm_ops = &rpi_gpiomem_vm_ops;
+ offset = vma->vm_start;
+ for (i = 0; i < priv->nr_wins; i++) {
+ base = priv->iowins[i].phys_base >> PAGE_SHIFT;
+ len = priv->iowins[i].len;
+ vma->vm_page_prot = phys_mem_access_prot(file, base, len,
+ vma->vm_page_prot);
+ if (remap_pfn_range(vma, offset,
+ base, len,
+ vma->vm_page_prot))
+ break;
+ offset += len;
+ }
+
+ if (i < priv->nr_wins)
+ return -EAGAIN;
+
+ return 0;
+}
+
+static const struct file_operations rpi_gpiomem_fops = {
+ .owner = THIS_MODULE,
+ .open = rpi_gpiomem_open,
+ .release = rpi_gpiomem_release,
+ .mmap = rpi_gpiomem_mmap,
+};
+
+static const struct of_device_id rpi_gpiomem_of_match[];
+
+static int rpi_gpiomem_probe(struct platform_device *pdev)
+{
+ int err, i;
+ const struct of_device_id *id;
+ struct device *dev = &pdev->dev;
+ struct device_node *node = dev->of_node;
+ struct resource *ioresource;
+ struct rpi_gpiomem_priv *priv;
+
+ /* Allocate buffers and instance data */
+
+ priv = kzalloc(sizeof(struct rpi_gpiomem_priv), GFP_KERNEL);
+
+ if (!priv) {
+ err = -ENOMEM;
+ goto failed_inst_alloc;
+ }
+ platform_set_drvdata(pdev, priv);
+
+ priv->dev = dev;
+ id = of_match_device(rpi_gpiomem_of_match, dev);
+ if (!id)
+ return -EINVAL;
+
+ /*
+ * Device node naming - for legacy (bcm2835) DT bindings, the driver
+ * created the node based on a hardcoded name - for new bindings,
+ * take the node name from DT.
+ */
+ if (id == &rpi_gpiomem_of_match[0]) {
+ priv->name = "gpiomem";
+ } else {
+ err = of_property_read_string(node, "chardev-name", &priv->name);
+ if (err)
+ return -EINVAL;
+ }
+
+ /*
+ * Go find the register ranges associated with this instance
+ */
+ for (i = 0; i < MAX_RANGES; i++) {
+ ioresource = platform_get_resource(pdev, IORESOURCE_MEM, i);
+ if (!ioresource && i == 0) {
+ dev_err(priv->dev, "failed to get IO resource - no ranges available\n");
+ err = -ENOENT;
+ goto failed_get_resource;
+ }
+ if (!ioresource)
+ break;
+
+ priv->iowins[i].phys_base = ioresource->start;
+ priv->iowins[i].len = (ioresource->end + 1) - ioresource->start;
+ dev_info(&pdev->dev, "window base 0x%08lx size 0x%08lx\n",
+ priv->iowins[i].phys_base, priv->iowins[i].len);
+ priv->nr_wins++;
+ }
+
+ /* Create character device entries */
+
+ err = alloc_chrdev_region(&priv->devid,
+ DEVICE_MINOR, 1, priv->name);
+ if (err != 0) {
+ dev_err(priv->dev, "unable to allocate device number");
+ goto failed_alloc_chrdev;
+ }
+ cdev_init(&priv->rpi_gpiomem_cdev, &rpi_gpiomem_fops);
+ priv->rpi_gpiomem_cdev.owner = THIS_MODULE;
+ err = cdev_add(&priv->rpi_gpiomem_cdev, priv->devid, 1);
+ if (err != 0) {
+ dev_err(priv->dev, "unable to register device");
+ goto failed_cdev_add;
+ }
+
+ /* Create sysfs entries */
+
+ priv->class = class_create(priv->name);
+ if (IS_ERR(priv->class)) {
+ err = PTR_ERR(priv->class);
+ goto failed_class_create;
+ }
+
+ dev = device_create(priv->class, NULL, priv->devid, NULL, priv->name);
+ if (IS_ERR(dev)) {
+ err = PTR_ERR(dev);
+ goto failed_device_create;
+ }
+
+ dev_info(priv->dev, "initialised %u regions as /dev/%s\n",
+ priv->nr_wins, priv->name);
+
+ return 0;
+
+failed_device_create:
+ class_destroy(priv->class);
+failed_class_create:
+ cdev_del(&priv->rpi_gpiomem_cdev);
+failed_cdev_add:
+ unregister_chrdev_region(priv->devid, 1);
+failed_alloc_chrdev:
+failed_get_resource:
+ kfree(priv);
+failed_inst_alloc:
+ dev_err(&pdev->dev, "could not load rpi_gpiomem");
+ return err;
+}
+
+static void rpi_gpiomem_remove(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct rpi_gpiomem_priv *priv = platform_get_drvdata(pdev);
+
+ device_destroy(priv->class, priv->devid);
+ class_destroy(priv->class);
+ cdev_del(&priv->rpi_gpiomem_cdev);
+ unregister_chrdev_region(priv->devid, 1);
+ kfree(priv);
+
+ dev_info(dev, "%s driver removed - OK", priv->name);
+}
+
+static const struct of_device_id rpi_gpiomem_of_match[] = {
+ {
+ .compatible = "brcm,bcm2835-gpiomem",
+ },
+ {
+ .compatible = "raspberrypi,gpiomem",
+ },
+ { /* sentinel */ },
+};
+
+MODULE_DEVICE_TABLE(of, rpi_gpiomem_of_match);
+
+static struct platform_driver rpi_gpiomem_driver = {
+ .probe = rpi_gpiomem_probe,
+ .remove = rpi_gpiomem_remove,
+ .driver = {
+ .name = DRIVER_NAME,
+ .owner = THIS_MODULE,
+ .of_match_table = rpi_gpiomem_of_match,
+ },
+};
+
+module_platform_driver(rpi_gpiomem_driver);
+
+MODULE_ALIAS("platform:rpi-gpiomem");
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("Driver for accessing GPIOs from userspace");
+MODULE_AUTHOR("Jonathan Bell <jonathan@raspberrypi.com>");