Added driver to use rpmsg with gpiochip interface.Requires PRU firmware

Please follow instructions to load PRU firmware
https://github.com/deebot/Beaglebone-BidirectionBus/blob/dev/bidirec_299/README.md

(cherry picked from commit 66cbf64)

Author: deebot

drivers/rpmsg/rpmsg_gpio.c

@@ -0,0 +1,222 @@
+/*
+ * PRU Remote Processor Messaging Driver with gpiochip interface
+ * copyright (c) 2020 Deepankar Maithani
+ * Codes examples from Lab no 5 from TI and has been used as boiler plate for rpmsg communication
+ * https://processors.wiki.ti.com/index.php/PRU_Training:_Hands-on_Labs
+ *
+ * For learn more about the complete project visit:
+ * https://github.com/deebot/Beaglebone-BidirectionBus/tree/dev
+ * Steps to test the driver.
+ * https://github.com/deebot/Beaglebone-BidirectionBus/blob/dev/bidirec_299/README.md
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/gpio.h>
+#include <linux/of.h>
+#include <linux/rpmsg.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kfifo.h>
+#include <linux/uaccess.h>
+#include <linux/poll.h>
+#include <linux/rpmsg/virtio_rpmsg.h>
+#include <linux/stat.h>
+#include <linux/bitops.h>
+#define PRU_MAX_DEVICES				(16)
+/* Matches the definition in virtio_rpmsg_bus.c */
+#define RPMSG_BUF_SIZE				(512)
+#define MAX_FIFO_MSG				(32)
+#define FIFO_MSG_SIZE				RPMSG_BUF_SIZE
+#define GPIO_NUM 9
+static DEFINE_MUTEX(rpmsg_pru_lock);
+static char rpmsg_pru_buf[RPMSG_BUF_SIZE];
+static struct gpio_chip chip;
+struct rpmsg_pru_dev {
+	struct rpmsg_device *rpdev;
+	struct device *dev;
+	bool locked;
+	dev_t devt;
+	struct kfifo msg_fifo;
+	u32 msg_len[MAX_FIFO_MSG];
+	int msg_idx_rd;
+	int msg_idx_wr;
+	wait_queue_head_t wait_list;
+	uint32_t gpio_state;
+	long input_state;
+
+};
+
+struct rpmsg_pru_dev *prudev;
+/*Reads the lines which are  set as input*/
+static int mygpio_get_value(struct gpio_chip *gc, unsigned offset)
+{
+	uint32_t value;
+	struct rpmsg_device *rpdev = container_of(gc->parent,
+			struct rpmsg_device, dev);
+	unsigned int mask = BIT(offset % 8);
+	prudev = dev_get_drvdata(&rpdev->dev);
+
+	value = (prudev->input_state & mask)>>offset;
+	return value;
+}
+/* Writes to the lines and creates the gpio_state which is then sent as RPmsg */
+static void mygpio_set_value(struct gpio_chip *gc, unsigned offset, int val)
+{
+	int ret;
+	struct rpmsg_device *rpdev = container_of(gc->parent, struct rpmsg_device, dev);
+	pr_info("set_value function triggered");
+	pr_info("The bit number %d is set to value: %d", offset, val);
+
+	prudev = dev_get_drvdata(&rpdev->dev);
+	if (val == 0) {
+		prudev->gpio_state &= ~(1<<offset);
+	} else {
+		prudev->gpio_state |= (1<<offset);
+	}
+	if (offset == GPIO_NUM-1) {
+		/* copy the gpiostate in rpmsg buffer which will be sent over to PRU*/
+		memcpy((void *)&rpmsg_pru_buf, (void *)&(prudev->gpio_state),
+				 sizeof(&(prudev->gpio_state)));
+		pr_info("A check for checking gpio_state: %d",
+				prudev->gpio_state);
+		/* This line actually sends the data to the other side*/
+		ret = rpmsg_send(rpdev->ept, (void *)rpmsg_pru_buf, 2);
+		if (ret)
+			dev_err(gc->parent, "rpmsg_send failed: %d\n", ret);
+	}
+
+}
+
+/*sets the  pin to output. Will be called when user sets one
+ * of the gpiochip line as output which can be done manually
+ * in sysfs or using libgpiod */
+
+static int mygpio_direction_output(struct gpio_chip *gc,
+				       unsigned offset, int val)
+{
+	pr_info("Direction of GPIO set to: out\n");
+	return 0;
+}
+/*Runs When direction of a line is set as output*/
+static int mygpio_direction_input(struct gpio_chip *gc,
+				       unsigned offset)
+{
+
+	pr_info("Direction of GPIO set to: in \n");
+    return 0;
+}
+/*This function gets called every time
+ *an rpmsg_channel is created with a name that matches the .name
+ *attribute of the rpmsg_driver_sample_id_table. It sets up suitable memory
+ *and the gpiochip interface that can be seen in /sys/class/gpio and /dev.
+ */
+static int mygpio_rpmsg_pru_probe (struct rpmsg_device *rpdev)
+{
+	int ret;
+	struct rpmsg_pru_dev *prudev;
+	prudev = devm_kzalloc(&rpdev->dev, sizeof(*prudev), GFP_KERNEL);
+	if (!prudev)
+		return -ENOMEM;
+	prudev->rpdev = rpdev;
+	ret = kfifo_alloc(&prudev->msg_fifo, MAX_FIFO_MSG * FIFO_MSG_SIZE,
+				  GFP_KERNEL);
+	if (ret) {
+			dev_err(&rpdev->dev, "Unable to allocate fifo for the rpmsg_pru device\n");
+			return -ENOMEM;
+		}
+	init_waitqueue_head(&prudev->wait_list);
+	dev_set_drvdata(&rpdev->dev, prudev);
+	chip.label = rpdev->desc;
+	chip.base = -1;
+	chip.parent = &rpdev->dev;
+	chip.owner = THIS_MODULE;
+	chip.ngpio = GPIO_NUM;
+	chip.can_sleep = 1;
+	chip.get = mygpio_get_value;
+	chip.set = mygpio_set_value;
+	chip.direction_output = mygpio_direction_output;
+	chip.direction_input = mygpio_direction_input;
+	return gpiochip_add(&chip);
+}
+/* Callback function which gets called whenever a new rpmsg is received
+ * The data received from the PRU is converted into long and then assigned to
+ * input_state
+ * @msg_fifo: kernel fifo used to buffer the messages between userspace and PRU
+ * @msg_len: array storing the lengths of each message in the kernel fifo
+ * @msg_idx_rd: kernel fifo read index
+ * @msg_idx_wr: kernel fifo write index
+ * */
+static int mygpio_rpmsg_pru_cb(struct rpmsg_device *rpdev, void *data, int len,
+			void *priv, u32 src)
+{  int ret;
+	u32 length;
+	struct rpmsg_pru_dev *prudev;
+
+	prudev = dev_get_drvdata(&rpdev->dev);
+
+	if (kfifo_avail(&prudev->msg_fifo) < len) {
+		dev_err(&rpdev->dev, "Not enough space on the FIFO\n");
+		return -ENOSPC;
+	}
+
+	if ((prudev->msg_idx_wr + 1) % MAX_FIFO_MSG ==
+		prudev->msg_idx_rd) {
+		dev_err(&rpdev->dev, "Message length table is full\n");
+		return -ENOSPC;
+	}
+   /* adds the data received into a fifo*/
+	length = kfifo_in(&prudev->msg_fifo, data, len);
+	prudev->msg_len[prudev->msg_idx_wr] = length;
+	prudev->msg_idx_wr = (prudev->msg_idx_wr + 1) % MAX_FIFO_MSG;
+
+	wake_up_interruptible(&prudev->wait_list);
+	ret = kstrtol((char *) data, 10, &prudev->input_state);
+	if (ret) {
+	return ret;
+	}
+	pr_info("The shift register port state is: %ld", prudev->input_state);
+	return 0;
+}
+static void mygpio_rpmsg_pru_remove(struct rpmsg_device *rpdev)
+{
+	struct rpmsg_pru_dev *prudev;
+	prudev = dev_get_drvdata(&rpdev->dev);
+
+	kfifo_free(&prudev->msg_fifo);
+	gpiochip_remove(&chip);
+
+}
+/*
+ * Matches this tag:If you change .name
+ * PRU firmware should also be updated with same channel name
+ */
+static const struct rpmsg_device_id rpmsg_driver_pru_id_table[] = {
+	{ .name	= "rpmsg-pru-gpio" },
+	{ },
+};
+MODULE_DEVICE_TABLE(rpmsg, rpmsg_driver_pru_id_table);
+
+static struct rpmsg_driver rpmsg_pru_driver = {
+	.drv.name	= KBUILD_MODNAME,
+	.id_table	= rpmsg_driver_pru_id_table,
+	.probe		= mygpio_rpmsg_pru_probe,
+	.callback	= mygpio_rpmsg_pru_cb,
+	.remove		= mygpio_rpmsg_pru_remove,
+};
+
+module_rpmsg_driver(rpmsg_pru_driver);
+MODULE_AUTHOR("DeepankarMaithani <[email protected]>");
+MODULE_DESCRIPTION("A driver to send rpmsg data using sysfs and chardev interface");
+MODULE_VERSION("0.1");
+MODULE_LICENSE("GPL");
+