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

@@ -425,4 +425,12 @@ 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

@@ -45,3 +45,4 @@ 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>");