[PATCH V5 0/2] gpio: Add virtio based driver

[PATCH V5 0/2] gpio: Add virtio based driver

[Viresh Kumar]

Hello,

This adds Virtio GPIO driver based on the proposed specification [1].

The specification for basic GPIO operations is already reviewed by Linus and
Arnd, while the IRQ stuff is still under discussion and not finalized.

I am sharing the code, so everyone gets more clarity on how it will work
eventually in Linux.

I have tested this patchset with Qemu guest with help of the libgpiod utility.
I have also tested basic handling of interrupts on the guest side. It works as
expected.

The host side virtio-backend isn't ready yet and my tests only tested the flow
control between guest and host, but didn't play with real GPIO pins.  That will
be done once I have a working backend in place (WIP).

V4->V5:
- Use ____cacheline_aligned for buffers.
- Proper locking in place, which avoids the use of work-item for processing
  interrupts.
- Separate callbacks for enable/disable of irqs.
- The irq is disabled at the host only for enable/disable now, instead of
  mask/unmask.
- mask/unmask only control the queuing of buffers now.
- Use handle_level_irq() instead of handle_fasteoi_irq().
- Other minor changes.

V3->V4:
- Lots of changes, as the specification changed too much. Better forget
  everything we have done until now :)

--
Viresh

[1] https://lists.oasis-open.org/archives/virtio-dev/202107/msg00232.html

Viresh Kumar (2):
  gpio: Add virtio-gpio driver
  gpio: virtio: Add IRQ support

 MAINTAINERS                      |   7 +
 drivers/gpio/Kconfig             |  10 +
 drivers/gpio/Makefile            |   1 +
 drivers/gpio/gpio-virtio.c       | 668 +++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_gpio.h |  72 ++++
 5 files changed, 758 insertions(+)
 create mode 100644 drivers/gpio/gpio-virtio.c
 create mode 100644 include/uapi/linux/virtio_gpio.h

-- 
2.31.1.272.g89b43f80a514

[PATCH V5 1/2] gpio: Add virtio-gpio driver

[Viresh Kumar]

This patch adds a new driver for Virtio based GPIO devices.

This allows a guest VM running Linux to access GPIO lines provided by
the host. It supports all basic operations, except interrupts for the
GPIO lines.

Based on the initial work posted by:
"Enrico Weigelt, metux IT consult" <lkml@metux.net>.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
Enrico, lemme know if you want me to add your co-developed by and
signed-off-by. Didn't want to add without checking with you first.
---
 MAINTAINERS                      |   7 +
 drivers/gpio/Kconfig             |   9 +
 drivers/gpio/Makefile            |   1 +
 drivers/gpio/gpio-virtio.c       | 375 +++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_gpio.h |  47 ++++
 5 files changed, 439 insertions(+)
 create mode 100644 drivers/gpio/gpio-virtio.c
 create mode 100644 include/uapi/linux/virtio_gpio.h

diff --git a/MAINTAINERS b/MAINTAINERS
index a61f4f3b78a9..f632acd7d98c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -19647,6 +19647,13 @@ F:	Documentation/filesystems/virtiofs.rst
 F:	fs/fuse/virtio_fs.c
 F:	include/uapi/linux/virtio_fs.h
 
+VIRTIO GPIO DRIVER
+M:	Enrico Weigelt, metux IT consult <info@metux.net>
+M:	Viresh Kumar <vireshk@kernel.org>
+S:	Maintained
+F:	drivers/gpio/gpio-virtio.c
+F:	include/uapi/linux/virtio_gpio.h
+
 VIRTIO GPU DRIVER
 M:	David Airlie <airlied@linux.ie>
 M:	Gerd Hoffmann <kraxel@redhat.com>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index fab571016adf..e5993d6864fb 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1669,6 +1669,15 @@ config GPIO_MOCKUP
 	  tools/testing/selftests/gpio/gpio-mockup.sh. Reference the usage in
 	  it.
 
+config GPIO_VIRTIO
+	tristate "VirtIO GPIO support"
+	depends on VIRTIO
+	help
+	  Say Y here to enable guest support for virtio-based GPIO controllers.
+
+	  These virtual GPIOs can be routed to real GPIOs or attached to
+	  simulators on the host (like QEMU).
+
 endmenu
 
 endif
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 32a32659866a..e0301cfedd8d 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -165,6 +165,7 @@ obj-$(CONFIG_GPIO_UCB1400)		+= gpio-ucb1400.o
 obj-$(CONFIG_GPIO_UNIPHIER)		+= gpio-uniphier.o
 obj-$(CONFIG_GPIO_VF610)		+= gpio-vf610.o
 obj-$(CONFIG_GPIO_VIPERBOARD)		+= gpio-viperboard.o
+obj-$(CONFIG_GPIO_VIRTIO)		+= gpio-virtio.o
 obj-$(CONFIG_GPIO_VISCONTI)		+= gpio-visconti.o
 obj-$(CONFIG_GPIO_VR41XX)		+= gpio-vr41xx.o
 obj-$(CONFIG_GPIO_VX855)		+= gpio-vx855.o
diff --git a/drivers/gpio/gpio-virtio.c b/drivers/gpio/gpio-virtio.c
new file mode 100644
index 000000000000..4dc2d383508f
--- /dev/null
+++ b/drivers/gpio/gpio-virtio.c
@@ -0,0 +1,375 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * GPIO driver for virtio-based virtual GPIO controllers
+ *
+ * Copyright (C) 2021 metux IT consult
+ * Enrico Weigelt, metux IT consult <info@metux.net>
+ *
+ * Copyright (C) 2021 Linaro.
+ * Viresh Kumar <viresh.kumar@linaro.org>
+ */
+
+#include <linux/completion.h>
+#include <linux/err.h>
+#include <linux/gpio/driver.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/virtio_config.h>
+#include <uapi/linux/virtio_gpio.h>
+#include <uapi/linux/virtio_ids.h>
+
+struct virtio_gpio_line {
+	struct mutex lock; /* Protects line operation */
+	struct completion completion;
+	struct virtio_gpio_request req ____cacheline_aligned;
+	struct virtio_gpio_response res ____cacheline_aligned;
+	unsigned int rxlen;
+};
+
+struct virtio_gpio {
+	struct virtio_device *vdev;
+	struct mutex lock; /* Protects virtqueue operation */
+	struct gpio_chip gc;
+	struct virtio_gpio_config config;
+	struct virtio_gpio_line *lines;
+	struct virtqueue *request_vq;
+};
+
+static int _virtio_gpio_req(struct virtio_gpio *vgpio, u16 type, u16 gpio,
+			    u8 txvalue, u8 *rxvalue, void *response, u32 rxlen)
+{
+	struct virtio_gpio_line *line = &vgpio->lines[gpio];
+	struct virtio_gpio_request *req = &line->req;
+	struct virtio_gpio_response *res = response;
+	struct scatterlist *sgs[2], req_sg, res_sg;
+	struct device *dev = &vgpio->vdev->dev;
+	int ret;
+
+	/*
+	 * Prevent concurrent requests for the same line since we have
+	 * pre-allocated request/response buffers for each GPIO line. Moreover
+	 * Linux always accesses a GPIO line sequentially, so this locking shall
+	 * always go through without any delays.
+	 */
+	mutex_lock(&line->lock);
+
+	req->type = cpu_to_le16(type);
+	req->gpio = cpu_to_le16(gpio);
+	req->value = txvalue;
+
+	sg_init_one(&req_sg, req, sizeof(*req));
+	sg_init_one(&res_sg, res, rxlen);
+	sgs[0] = &req_sg;
+	sgs[1] = &res_sg;
+
+	line->rxlen = 0;
+	reinit_completion(&line->completion);
+
+	/*
+	 * Virtqueue callers need to ensure they don't call its APIs with other
+	 * virtqueue operations at the same time.
+	 */
+	mutex_lock(&vgpio->lock);
+	ret = virtqueue_add_sgs(vgpio->request_vq, sgs, 1, 1, line, GFP_KERNEL);
+	if (ret) {
+		dev_err(dev, "failed to add request to vq\n");
+		mutex_unlock(&vgpio->lock);
+		goto out;
+	}
+
+	virtqueue_kick(vgpio->request_vq);
+	mutex_unlock(&vgpio->lock);
+
+	if (!wait_for_completion_timeout(&line->completion, HZ)) {
+		dev_err(dev, "GPIO operation timed out\n");
+		ret = -ETIMEDOUT;
+		goto out;
+	}
+
+	if (unlikely(res->status != VIRTIO_GPIO_STATUS_OK)) {
+		dev_err(dev, "GPIO request failed: %d\n", gpio);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (unlikely(line->rxlen != rxlen)) {
+		dev_err(dev, "GPIO operation returned incorrect len (%u : %u)\n",
+			rxlen, line->rxlen);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (rxvalue)
+		*rxvalue = res->value;
+
+out:
+	mutex_unlock(&line->lock);
+	return ret;
+}
+
+static int virtio_gpio_req(struct virtio_gpio *vgpio, u16 type, u16 gpio,
+			   u8 txvalue, u8 *rxvalue)
+{
+	struct virtio_gpio_line *line = &vgpio->lines[gpio];
+	struct virtio_gpio_response *res = &line->res;
+
+	return _virtio_gpio_req(vgpio, type, gpio, txvalue, rxvalue, res,
+				sizeof(*res));
+}
+
+static void virtio_gpio_free(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+
+	virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_SET_DIRECTION, gpio,
+			VIRTIO_GPIO_DIRECTION_NONE, NULL);
+}
+
+static int virtio_gpio_get_direction(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	u8 direction;
+	int ret;
+
+	ret = virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_GET_DIRECTION, gpio, 0,
+			      &direction);
+	if (ret)
+		return ret;
+
+	switch (direction) {
+	case VIRTIO_GPIO_DIRECTION_IN:
+		return GPIO_LINE_DIRECTION_IN;
+	case VIRTIO_GPIO_DIRECTION_OUT:
+		return GPIO_LINE_DIRECTION_OUT;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int virtio_gpio_direction_input(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+
+	return virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_SET_DIRECTION, gpio,
+			       VIRTIO_GPIO_DIRECTION_IN, NULL);
+}
+
+static int virtio_gpio_direction_output(struct gpio_chip *gc, unsigned int gpio,
+					int value)
+{
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	int ret;
+
+	ret = virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_SET_VALUE, gpio, value, NULL);
+	if (ret)
+		return ret;
+
+	return virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_SET_DIRECTION, gpio,
+			       VIRTIO_GPIO_DIRECTION_OUT, NULL);
+}
+
+static int virtio_gpio_get(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	u8 value;
+	int ret;
+
+	ret = virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_GET_VALUE, gpio, 0, &value);
+	return ret ? ret : value;
+}
+
+static void virtio_gpio_set(struct gpio_chip *gc, unsigned int gpio, int value)
+{
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+
+	virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_SET_VALUE, gpio, value, NULL);
+}
+
+static void virtio_gpio_request_vq(struct virtqueue *vq)
+{
+	struct virtio_gpio_line *line;
+	unsigned int len;
+
+	do {
+		line = virtqueue_get_buf(vq, &len);
+		if (!line)
+			return;
+
+		line->rxlen = len;
+		complete(&line->completion);
+	} while (1);
+}
+
+static void virtio_gpio_free_vqs(struct virtio_device *vdev)
+{
+	vdev->config->reset(vdev);
+	vdev->config->del_vqs(vdev);
+}
+
+static int virtio_gpio_alloc_vqs(struct virtio_gpio *vgpio,
+				 struct virtio_device *vdev)
+{
+	const char * const names[] = { "requestq" };
+	vq_callback_t *cbs[] = {
+		virtio_gpio_request_vq,
+	};
+	struct virtqueue *vqs[1] = { NULL };
+	int ret;
+
+	ret = virtio_find_vqs(vdev, 1, vqs, cbs, names, NULL);
+	if (ret) {
+		dev_err(&vdev->dev, "failed to find vqs: %d\n", ret);
+		return ret;
+	}
+
+	if (!vqs[0]) {
+		dev_err(&vdev->dev, "failed to find requestq vq\n");
+		return -ENODEV;
+	}
+	vgpio->request_vq = vqs[0];
+
+	return 0;
+}
+
+static const char **virtio_gpio_get_names(struct virtio_gpio *vgpio)
+{
+	struct virtio_gpio_config *config = &vgpio->config;
+	struct virtio_gpio_response_get_names *res;
+	struct device *dev = &vgpio->vdev->dev;
+	u8 *gpio_names, *str;
+	const char **names;
+	int i, ret, len;
+
+	if (!config->gpio_names_size)
+		return NULL;
+
+	len = sizeof(*res) + config->gpio_names_size;
+	res = devm_kzalloc(dev, len, GFP_KERNEL);
+	if (!res)
+		return NULL;
+	gpio_names = res->value;
+
+	ret = _virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_GET_NAMES, 0, 0, NULL,
+			       res, len);
+	if (ret) {
+		dev_err(dev, "Failed to get GPIO names: %d\n", ret);
+		return NULL;
+	}
+
+	names = devm_kcalloc(dev, config->ngpio, sizeof(names), GFP_KERNEL);
+	if (!names)
+		return NULL;
+
+	/* NULL terminate the string instead of checking it */
+	gpio_names[config->gpio_names_size - 1] = '\0';
+
+	for (i = 0, str = gpio_names; i < config->ngpio; i++) {
+		names[i] = str;
+		str += strlen(str) + 1; /* zero-length strings are allowed */
+
+		if (str > gpio_names + config->gpio_names_size) {
+			dev_err(dev, "gpio_names block is too short (%d)\n", i);
+			return NULL;
+		}
+	}
+
+	return names;
+}
+
+static int virtio_gpio_probe(struct virtio_device *vdev)
+{
+	struct virtio_gpio_config *config;
+	struct device *dev = &vdev->dev;
+	struct virtio_gpio *vgpio;
+	int ret, i;
+
+	vgpio = devm_kzalloc(dev, sizeof(*vgpio), GFP_KERNEL);
+	if (!vgpio)
+		return -ENOMEM;
+
+	config = &vgpio->config;
+
+	/* Read configuration */
+	virtio_cread_bytes(vdev, 0, config, sizeof(*config));
+	config->gpio_names_size = le32_to_cpu(config->gpio_names_size);
+	config->ngpio = le16_to_cpu(config->ngpio);
+	if (!config->ngpio) {
+		dev_err(dev, "Number of GPIOs can't be zero\n");
+		return -EINVAL;
+	}
+
+	vgpio->lines = devm_kcalloc(dev, config->ngpio, sizeof(*vgpio->lines), GFP_KERNEL);
+	if (!vgpio->lines)
+		return -ENOMEM;
+
+	for (i = 0; i < config->ngpio; i++) {
+		mutex_init(&vgpio->lines[i].lock);
+		init_completion(&vgpio->lines[i].completion);
+	}
+
+	mutex_init(&vgpio->lock);
+	vdev->priv = vgpio;
+
+	vgpio->vdev			= vdev;
+	vgpio->gc.free			= virtio_gpio_free;
+	vgpio->gc.get_direction		= virtio_gpio_get_direction;
+	vgpio->gc.direction_input	= virtio_gpio_direction_input;
+	vgpio->gc.direction_output	= virtio_gpio_direction_output;
+	vgpio->gc.get			= virtio_gpio_get;
+	vgpio->gc.set			= virtio_gpio_set;
+	vgpio->gc.ngpio			= config->ngpio;
+	vgpio->gc.base			= -1; /* Allocate base dynamically */
+	vgpio->gc.label			= dev_name(dev);
+	vgpio->gc.parent		= dev;
+	vgpio->gc.owner			= THIS_MODULE;
+	vgpio->gc.can_sleep		= true;
+
+	ret = virtio_gpio_alloc_vqs(vgpio, vdev);
+	if (ret)
+		return ret;
+
+	/* Mark the device ready to perform operations from within probe() */
+	virtio_device_ready(vdev);
+
+	vgpio->gc.names = virtio_gpio_get_names(vgpio);
+
+	ret = gpiochip_add_data(&vgpio->gc, vgpio);
+	if (ret) {
+		virtio_gpio_free_vqs(vdev);
+		dev_err(dev, "Failed to add virtio-gpio controller\n");
+	}
+
+	return ret;
+}
+
+static void virtio_gpio_remove(struct virtio_device *vdev)
+{
+	struct virtio_gpio *vgpio = vdev->priv;
+
+	gpiochip_remove(&vgpio->gc);
+	virtio_gpio_free_vqs(vdev);
+}
+
+static const struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_GPIO, VIRTIO_DEV_ANY_ID },
+	{},
+};
+MODULE_DEVICE_TABLE(virtio, id_table);
+
+static struct virtio_driver virtio_gpio_driver = {
+	.id_table		= id_table,
+	.probe			= virtio_gpio_probe,
+	.remove			= virtio_gpio_remove,
+	.driver			= {
+		.name		= KBUILD_MODNAME,
+		.owner		= THIS_MODULE,
+	},
+};
+module_virtio_driver(virtio_gpio_driver);
+
+MODULE_AUTHOR("Enrico Weigelt, metux IT consult <info@metux.net>");
+MODULE_AUTHOR("Viresh Kumar <viresh.kumar@linaro.org>");
+MODULE_DESCRIPTION("VirtIO GPIO driver");
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/linux/virtio_gpio.h b/include/uapi/linux/virtio_gpio.h
new file mode 100644
index 000000000000..844574acf095
--- /dev/null
+++ b/include/uapi/linux/virtio_gpio.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+
+#ifndef _LINUX_VIRTIO_GPIO_H
+#define _LINUX_VIRTIO_GPIO_H
+
+#include <linux/types.h>
+
+/* Virtio GPIO request types */
+#define VIRTIO_GPIO_MSG_GET_NAMES		0x0001
+#define VIRTIO_GPIO_MSG_GET_DIRECTION		0x0002
+#define VIRTIO_GPIO_MSG_SET_DIRECTION		0x0003
+#define VIRTIO_GPIO_MSG_GET_VALUE		0x0004
+#define VIRTIO_GPIO_MSG_SET_VALUE		0x0005
+
+/* Possible values of the status field */
+#define VIRTIO_GPIO_STATUS_OK			0x0
+#define VIRTIO_GPIO_STATUS_ERR			0x1
+
+/* Direction types */
+#define VIRTIO_GPIO_DIRECTION_NONE		0x00
+#define VIRTIO_GPIO_DIRECTION_OUT		0x01
+#define VIRTIO_GPIO_DIRECTION_IN		0x02
+
+struct virtio_gpio_config {
+	__u16 ngpio;
+	__u8 padding[2];
+	__u32 gpio_names_size;
+} __packed;
+
+/* Virtio GPIO Request / Response */
+struct virtio_gpio_request {
+	__u16 type;
+	__u16 gpio;
+	__u32 value;
+};
+
+struct virtio_gpio_response {
+	__u8 status;
+	__u8 value;
+};
+
+struct virtio_gpio_response_get_names {
+	__u8 status;
+	__u8 value[];
+};
+
+#endif /* _LINUX_VIRTIO_GPIO_H */
-- 
2.31.1.272.g89b43f80a514

[PATCH V5 2/2] gpio: virtio: Add IRQ support

[Viresh Kumar]

This patch adds IRQ support for the virtio GPIO driver. Note that this
uses the irq_bus_lock/unlock() callbacks, since those operations over
virtio may sleep. Also the notifications for the eventq are processed
using a work item to allow sleep-able operations.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/gpio/Kconfig             |   1 +
 drivers/gpio/gpio-virtio.c       | 301 ++++++++++++++++++++++++++++++-
 include/uapi/linux/virtio_gpio.h |  25 +++
 3 files changed, 323 insertions(+), 4 deletions(-)

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index e5993d6864fb..222f4ae98a35 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1672,6 +1672,7 @@ config GPIO_MOCKUP
 config GPIO_VIRTIO
 	tristate "VirtIO GPIO support"
 	depends on VIRTIO
+	select GPIOLIB_IRQCHIP
 	help
 	  Say Y here to enable guest support for virtio-based GPIO controllers.
 
diff --git a/drivers/gpio/gpio-virtio.c b/drivers/gpio/gpio-virtio.c
index 4dc2d383508f..0cb2c708c705 100644
--- a/drivers/gpio/gpio-virtio.c
+++ b/drivers/gpio/gpio-virtio.c
@@ -16,6 +16,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/spinlock.h>
 #include <linux/virtio_config.h>
 #include <uapi/linux/virtio_gpio.h>
 #include <uapi/linux/virtio_ids.h>
@@ -28,6 +29,17 @@ struct virtio_gpio_line {
 	unsigned int rxlen;
 };
 
+struct vgpio_irq_line {
+	u8 type;
+	bool disabled;
+	bool masked;
+	bool queued;
+	bool update_pending;
+
+	struct virtio_gpio_irq_request ireq ____cacheline_aligned;
+	struct virtio_gpio_irq_response ires ____cacheline_aligned;
+};
+
 struct virtio_gpio {
 	struct virtio_device *vdev;
 	struct mutex lock; /* Protects virtqueue operation */
@@ -35,6 +47,12 @@ struct virtio_gpio {
 	struct virtio_gpio_config config;
 	struct virtio_gpio_line *lines;
 	struct virtqueue *request_vq;
+
+	/* irq support */
+	struct virtqueue *event_vq;
+	struct mutex irq_lock; /* Protects irq operation */
+	spinlock_t eventq_lock; /* Protects queuing of the buffer */
+	struct vgpio_irq_line *irq_lines;
 };
 
 static int _virtio_gpio_req(struct virtio_gpio *vgpio, u16 type, u16 gpio,
@@ -187,6 +205,236 @@ static void virtio_gpio_set(struct gpio_chip *gc, unsigned int gpio, int value)
 	virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_SET_VALUE, gpio, value, NULL);
 }
 
+/* Interrupt handling */
+static void virtio_gpio_irq_prepare(struct virtio_gpio *vgpio, u16 gpio)
+{
+	struct vgpio_irq_line *irq_line = &vgpio->irq_lines[gpio];
+	struct virtio_gpio_irq_request *ireq = &irq_line->ireq;
+	struct virtio_gpio_irq_response *ires = &irq_line->ires;
+	struct scatterlist *sgs[2], req_sg, res_sg;
+	int ret;
+
+	if (WARN_ON(irq_line->queued || irq_line->masked || irq_line->disabled))
+		return;
+
+	ireq->gpio = cpu_to_le16(gpio);
+	sg_init_one(&req_sg, ireq, sizeof(*ireq));
+	sg_init_one(&res_sg, ires, sizeof(*ires));
+	sgs[0] = &req_sg;
+	sgs[1] = &res_sg;
+
+	ret = virtqueue_add_sgs(vgpio->event_vq, sgs, 1, 1, irq_line, GFP_ATOMIC);
+	if (ret) {
+		dev_err(&vgpio->vdev->dev, "failed to add request to eventq\n");
+		return;
+	}
+
+	irq_line->queued = true;
+	virtqueue_kick(vgpio->event_vq);
+}
+
+static void virtio_gpio_irq_enable(struct irq_data *d)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	struct vgpio_irq_line *irq_line = &vgpio->irq_lines[d->hwirq];
+
+	spin_lock(&vgpio->eventq_lock);
+	irq_line->disabled = false;
+	irq_line->masked = false;
+
+	/* Queue the buffer unconditionally on enable */
+	virtio_gpio_irq_prepare(vgpio, d->hwirq);
+	spin_unlock(&vgpio->eventq_lock);
+
+	irq_line->update_pending = true;
+}
+
+static void virtio_gpio_irq_disable(struct irq_data *d)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	struct vgpio_irq_line *irq_line = &vgpio->irq_lines[d->hwirq];
+
+	spin_lock(&vgpio->eventq_lock);
+	irq_line->disabled = true;
+	irq_line->masked = true;
+	spin_unlock(&vgpio->eventq_lock);
+
+	irq_line->update_pending = true;
+}
+
+static void virtio_gpio_irq_mask(struct irq_data *d)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	struct vgpio_irq_line *irq_line = &vgpio->irq_lines[d->hwirq];
+
+	spin_lock(&vgpio->eventq_lock);
+	irq_line->masked = true;
+	spin_unlock(&vgpio->eventq_lock);
+}
+
+static void virtio_gpio_irq_unmask(struct irq_data *d)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	struct vgpio_irq_line *irq_line = &vgpio->irq_lines[d->hwirq];
+
+	spin_lock(&vgpio->eventq_lock);
+	irq_line->masked = false;
+
+	/* Queue the buffer unconditionally on unmask */
+	virtio_gpio_irq_prepare(vgpio, d->hwirq);
+	spin_unlock(&vgpio->eventq_lock);
+}
+
+static int virtio_gpio_irq_set_type(struct irq_data *d, unsigned int type)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	struct vgpio_irq_line *irq_line = &vgpio->irq_lines[d->hwirq];
+
+	switch (type) {
+	case IRQ_TYPE_NONE:
+		type = VIRTIO_GPIO_IRQ_TYPE_NONE;
+		break;
+	case IRQ_TYPE_EDGE_RISING:
+		type = VIRTIO_GPIO_IRQ_TYPE_EDGE_RISING;
+		break;
+	case IRQ_TYPE_EDGE_FALLING:
+		type = VIRTIO_GPIO_IRQ_TYPE_EDGE_FALLING;
+		break;
+	case IRQ_TYPE_EDGE_BOTH:
+		type = VIRTIO_GPIO_IRQ_TYPE_EDGE_BOTH;
+		break;
+	case IRQ_TYPE_LEVEL_LOW:
+		type = VIRTIO_GPIO_IRQ_TYPE_LEVEL_LOW;
+		break;
+	case IRQ_TYPE_LEVEL_HIGH:
+		type = VIRTIO_GPIO_IRQ_TYPE_LEVEL_HIGH;
+		break;
+	default:
+		dev_err(&vgpio->vdev->dev, "unsupported irq type: %u\n", type);
+		return -EINVAL;
+	}
+
+	irq_line->type = type;
+	irq_line->update_pending = true;
+
+	return 0;
+}
+
+static void virtio_gpio_irq_bus_lock(struct irq_data *d)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+
+	mutex_lock(&vgpio->irq_lock);
+}
+
+static void virtio_gpio_irq_bus_sync_unlock(struct irq_data *d)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+	struct virtio_gpio *vgpio = gpiochip_get_data(gc);
+	struct vgpio_irq_line *irq_line = &vgpio->irq_lines[d->hwirq];
+	u8 type = irq_line->disabled ? VIRTIO_GPIO_IRQ_TYPE_NONE : irq_line->type;
+
+	if (irq_line->update_pending) {
+		irq_line->update_pending = false;
+		virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_IRQ_TYPE, d->hwirq, type,
+				NULL);
+	}
+
+	mutex_unlock(&vgpio->irq_lock);
+}
+
+static struct irq_chip vgpio_irq_chip = {
+	.name			= "virtio-gpio",
+	.irq_enable		= virtio_gpio_irq_enable,
+	.irq_disable		= virtio_gpio_irq_disable,
+	.irq_mask		= virtio_gpio_irq_mask,
+	.irq_unmask		= virtio_gpio_irq_unmask,
+	.irq_set_type		= virtio_gpio_irq_set_type,
+
+	/* These are required to implement irqchip for slow busses */
+	.irq_bus_lock		= virtio_gpio_irq_bus_lock,
+	.irq_bus_sync_unlock	= virtio_gpio_irq_bus_sync_unlock,
+};
+
+static bool ignore_irq(struct virtio_gpio *vgpio, int gpio,
+		       struct vgpio_irq_line *irq_line)
+{
+	bool ignore = false;
+
+	spin_lock(&vgpio->eventq_lock);
+	irq_line->queued = false;
+
+	/* Interrupt is disabled currently */
+	if (irq_line->masked || irq_line->disabled) {
+		ignore = true;
+		goto unlock;
+	}
+
+	/*
+	 * Buffer is returned as the interrupt was disabled earlier, but is
+	 * enabled again now. Requeue the buffers.
+	 */
+	if (irq_line->ires.status == VIRTIO_GPIO_IRQ_STATUS_INVALID) {
+		virtio_gpio_irq_prepare(vgpio, gpio);
+		ignore = true;
+		goto unlock;
+	}
+
+	if (WARN_ON(irq_line->ires.status != VIRTIO_GPIO_IRQ_STATUS_VALID))
+		ignore = true;
+
+unlock:
+	spin_unlock(&vgpio->eventq_lock);
+
+	return ignore;
+}
+
+static void virtio_gpio_event_vq(struct virtqueue *vq)
+{
+	struct virtio_gpio *vgpio = vq->vdev->priv;
+	struct device *dev = &vgpio->vdev->dev;
+	struct vgpio_irq_line *irq_line;
+	int irq, gpio, ret;
+	unsigned int len;
+
+	while (true) {
+		irq_line = virtqueue_get_buf(vgpio->event_vq, &len);
+		if (!irq_line)
+			break;
+
+		if (len != sizeof(irq_line->ires)) {
+			dev_err(dev, "irq with incorrect length (%u : %u)\n",
+				len, (unsigned int)sizeof(irq_line->ires));
+			continue;
+		}
+
+		/*
+		 * Find GPIO line number from the offset of irq_line within the
+		 * irq_lines block. We can also get GPIO number from
+		 * irq-request, but better not to rely on a buffer returned by
+		 * remote.
+		 */
+		gpio = irq_line - vgpio->irq_lines;
+		WARN_ON(gpio >= vgpio->config.ngpio);
+
+		if (unlikely(ignore_irq(vgpio, gpio, irq_line)))
+			continue;
+
+		irq = irq_find_mapping(vgpio->gc.irq.domain, gpio);
+		WARN_ON(!irq);
+
+		ret = generic_handle_irq(irq);
+		if (ret)
+			dev_err(dev, "failed to handle interrupt: %d\n", ret);
+	};
+}
+
 static void virtio_gpio_request_vq(struct virtqueue *vq)
 {
 	struct virtio_gpio_line *line;
@@ -211,14 +459,15 @@ static void virtio_gpio_free_vqs(struct virtio_device *vdev)
 static int virtio_gpio_alloc_vqs(struct virtio_gpio *vgpio,
 				 struct virtio_device *vdev)
 {
-	const char * const names[] = { "requestq" };
+	const char * const names[] = { "requestq", "eventq" };
 	vq_callback_t *cbs[] = {
 		virtio_gpio_request_vq,
+		virtio_gpio_event_vq,
 	};
-	struct virtqueue *vqs[1] = { NULL };
+	struct virtqueue *vqs[2] = { NULL, NULL };
 	int ret;
 
-	ret = virtio_find_vqs(vdev, 1, vqs, cbs, names, NULL);
+	ret = virtio_find_vqs(vdev, vgpio->irq_lines ? 2 : 1, vqs, cbs, names, NULL);
 	if (ret) {
 		dev_err(&vdev->dev, "failed to find vqs: %d\n", ret);
 		return ret;
@@ -226,11 +475,23 @@ static int virtio_gpio_alloc_vqs(struct virtio_gpio *vgpio,
 
 	if (!vqs[0]) {
 		dev_err(&vdev->dev, "failed to find requestq vq\n");
-		return -ENODEV;
+		goto out;
 	}
 	vgpio->request_vq = vqs[0];
 
+	if (vgpio->irq_lines && !vqs[1]) {
+		dev_err(&vdev->dev, "failed to find eventq vq\n");
+		goto out;
+	}
+	vgpio->event_vq = vqs[1];
+
 	return 0;
+
+out:
+	if (vqs[0] || vqs[1])
+		virtio_gpio_free_vqs(vdev);
+
+	return -ENODEV;
 }
 
 static const char **virtio_gpio_get_names(struct virtio_gpio *vgpio)
@@ -326,6 +587,32 @@ static int virtio_gpio_probe(struct virtio_device *vdev)
 	vgpio->gc.owner			= THIS_MODULE;
 	vgpio->gc.can_sleep		= true;
 
+	/* Interrupt support */
+	if (virtio_has_feature(vdev, VIRTIO_GPIO_F_IRQ)) {
+		vgpio->irq_lines = devm_kcalloc(dev, config->ngpio,
+						sizeof(*vgpio->irq_lines),
+						GFP_KERNEL);
+		if (!vgpio->irq_lines)
+			return -ENOMEM;
+
+		/* The event comes from the outside so no parent handler */
+		vgpio->gc.irq.parent_handler	= NULL;
+		vgpio->gc.irq.num_parents	= 0;
+		vgpio->gc.irq.parents		= NULL;
+		vgpio->gc.irq.default_type	= IRQ_TYPE_NONE;
+		vgpio->gc.irq.handler		= handle_level_irq;
+		vgpio->gc.irq.chip		= &vgpio_irq_chip;
+
+		for (i = 0; i < config->ngpio; i++) {
+			vgpio->irq_lines[i].type = VIRTIO_GPIO_IRQ_TYPE_NONE;
+			vgpio->irq_lines[i].disabled = true;
+			vgpio->irq_lines[i].masked = true;
+		}
+
+		mutex_init(&vgpio->irq_lock);
+		spin_lock_init(&vgpio->eventq_lock);
+	}
+
 	ret = virtio_gpio_alloc_vqs(vgpio, vdev);
 	if (ret)
 		return ret;
@@ -358,7 +645,13 @@ static const struct virtio_device_id id_table[] = {
 };
 MODULE_DEVICE_TABLE(virtio, id_table);
 
+static const unsigned int features[] = {
+	VIRTIO_GPIO_F_IRQ,
+};
+
 static struct virtio_driver virtio_gpio_driver = {
+	.feature_table		= features,
+	.feature_table_size	= ARRAY_SIZE(features),
 	.id_table		= id_table,
 	.probe			= virtio_gpio_probe,
 	.remove			= virtio_gpio_remove,
diff --git a/include/uapi/linux/virtio_gpio.h b/include/uapi/linux/virtio_gpio.h
index 844574acf095..297ffdae1a5d 100644
--- a/include/uapi/linux/virtio_gpio.h
+++ b/include/uapi/linux/virtio_gpio.h
@@ -5,12 +5,16 @@
 
 #include <linux/types.h>
 
+/* Virtio GPIO Feature bits */
+#define VIRTIO_GPIO_F_IRQ			0
+
 /* Virtio GPIO request types */
 #define VIRTIO_GPIO_MSG_GET_NAMES		0x0001
 #define VIRTIO_GPIO_MSG_GET_DIRECTION		0x0002
 #define VIRTIO_GPIO_MSG_SET_DIRECTION		0x0003
 #define VIRTIO_GPIO_MSG_GET_VALUE		0x0004
 #define VIRTIO_GPIO_MSG_SET_VALUE		0x0005
+#define VIRTIO_GPIO_MSG_IRQ_TYPE		0x0006
 
 /* Possible values of the status field */
 #define VIRTIO_GPIO_STATUS_OK			0x0
@@ -21,6 +25,14 @@
 #define VIRTIO_GPIO_DIRECTION_OUT		0x01
 #define VIRTIO_GPIO_DIRECTION_IN		0x02
 
+/* Virtio GPIO IRQ types */
+#define VIRTIO_GPIO_IRQ_TYPE_NONE		0x00
+#define VIRTIO_GPIO_IRQ_TYPE_EDGE_RISING	0x01
+#define VIRTIO_GPIO_IRQ_TYPE_EDGE_FALLING	0x02
+#define VIRTIO_GPIO_IRQ_TYPE_EDGE_BOTH		0x03
+#define VIRTIO_GPIO_IRQ_TYPE_LEVEL_HIGH		0x04
+#define VIRTIO_GPIO_IRQ_TYPE_LEVEL_LOW		0x08
+
 struct virtio_gpio_config {
 	__u16 ngpio;
 	__u8 padding[2];
@@ -44,4 +56,17 @@ struct virtio_gpio_response_get_names {
 	__u8 value[];
 };
 
+/* Virtio GPIO IRQ Request / Response */
+struct virtio_gpio_irq_request {
+	__u16 gpio;
+};
+
+struct virtio_gpio_irq_response {
+	__u8 status;
+};
+
+/* Possible values of the interrupt status field */
+#define VIRTIO_GPIO_IRQ_STATUS_INVALID		0x0
+#define VIRTIO_GPIO_IRQ_STATUS_VALID		0x1
+
 #endif /* _LINUX_VIRTIO_GPIO_H */
-- 
2.31.1.272.g89b43f80a514

Re: [PATCH V5 1/2] gpio: Add virtio-gpio driver

[Linus Walleij]

On Tue, Aug 10, 2021 at 12:25 PM Viresh Kumar <viresh.kumar@linaro.org> wrote:

> This patch adds a new driver for Virtio based GPIO devices.
>
> This allows a guest VM running Linux to access GPIO lines provided by
> the host. It supports all basic operations, except interrupts for the
> GPIO lines.
>
> Based on the initial work posted by:
> "Enrico Weigelt, metux IT consult" <lkml@metux.net>.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

I see there is a dependency that needs to be fixed but
the driver looks good to me:
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

Re: [PATCH V5 2/2] gpio: virtio: Add IRQ support

[Linus Walleij]

On Tue, Aug 10, 2021 at 12:25 PM Viresh Kumar <viresh.kumar@linaro.org> wrote:

> This patch adds IRQ support for the virtio GPIO driver. Note that this
> uses the irq_bus_lock/unlock() callbacks, since those operations over
> virtio may sleep. Also the notifications for the eventq are processed
> using a work item to allow sleep-able operations.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Looks good to me from a GPIO point of view:
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

Re: [PATCH V5 2/2] gpio: virtio: Add IRQ support

[Viresh Kumar]

On 10-08-21, 15:55, Viresh Kumar wrote:
> This patch adds IRQ support for the virtio GPIO driver. Note that this
> uses the irq_bus_lock/unlock() callbacks, since those operations over
> virtio may sleep. Also the notifications for the eventq are processed
> using a work item to allow sleep-able operations.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
>  drivers/gpio/Kconfig             |   1 +
>  drivers/gpio/gpio-virtio.c       | 301 ++++++++++++++++++++++++++++++-
>  include/uapi/linux/virtio_gpio.h |  25 +++
>  3 files changed, 323 insertions(+), 4 deletions(-)

Marc,

Will it be possible for you to have a look at this patch, it will help
us understand shortcomings of the specification better and this
implementation as well.

Thanks.

-- 
viresh