// 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/dma-mapping.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/spinlock.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;

        unsigned int rxlen;

        __dma_from_device_group_begin();
        struct virtio_gpio_request req;
        struct virtio_gpio_response res;
        __dma_from_device_group_end();
};

struct vgpio_irq_line {
        u8 type;
        bool disabled;
        bool masked;
        bool queued;
        bool update_pending;
        bool queue_pending;

        __dma_from_device_group_begin();
        struct virtio_gpio_irq_request ireq;
        struct virtio_gpio_irq_response ires;
        __dma_from_device_group_end();
};

struct virtio_gpio {
        struct virtio_device *vdev;
        struct mutex lock; /* Protects virtqueue operation */
        struct gpio_chip gc;
        struct virtio_gpio_line *lines;
        struct virtqueue *request_vq;

        /* irq support */
        struct virtqueue *event_vq;
        struct mutex irq_lock; /* Protects irq operation */
        raw_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,
                            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 = cpu_to_le32(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);

        wait_for_completion(&line->completion);

        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 int virtio_gpio_set(struct gpio_chip *gc, unsigned int gpio, int value)
{
        struct virtio_gpio *vgpio = gpiochip_get_data(gc);

        return 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];

        raw_spin_lock(&vgpio->eventq_lock);
        irq_line->disabled = false;
        irq_line->masked = false;
        irq_line->queue_pending = true;
        raw_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];

        raw_spin_lock(&vgpio->eventq_lock);
        irq_line->disabled = true;
        irq_line->masked = true;
        irq_line->queue_pending = false;
        raw_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];

        raw_spin_lock(&vgpio->eventq_lock);
        irq_line->masked = true;
        raw_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];

        raw_spin_lock(&vgpio->eventq_lock);
        irq_line->masked = false;

        /* Queue the buffer unconditionally on unmask */
        virtio_gpio_irq_prepare(vgpio, d->hwirq);
        raw_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_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;
        unsigned long flags;

        if (irq_line->update_pending) {
                irq_line->update_pending = false;
                virtio_gpio_req(vgpio, VIRTIO_GPIO_MSG_IRQ_TYPE, d->hwirq, type,
                                NULL);

                /* Queue the buffer only after interrupt is enabled */
                raw_spin_lock_irqsave(&vgpio->eventq_lock, flags);
                if (irq_line->queue_pending) {
                        irq_line->queue_pending = false;
                        virtio_gpio_irq_prepare(vgpio, d->hwirq);
                }
                raw_spin_unlock_irqrestore(&vgpio->eventq_lock, flags);
        }

        mutex_unlock(&vgpio->irq_lock);
}

static bool ignore_irq(struct virtio_gpio *vgpio, int gpio,
                       struct vgpio_irq_line *irq_line)
{
        bool ignore = false;

        raw_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:
        raw_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 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->gc.ngpio);

                if (unlikely(ignore_irq(vgpio, gpio, irq_line)))
                        continue;

                ret = generic_handle_domain_irq(vgpio->gc.irq.domain, gpio);
                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;
        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)
{
        virtio_reset_device(vdev);
        vdev->config->del_vqs(vdev);
}

static int virtio_gpio_alloc_vqs(struct virtio_gpio *vgpio,
                                 struct virtio_device *vdev)
{
        struct virtqueue_info vqs_info[] = {
                { "requestq", virtio_gpio_request_vq },
                { "eventq", virtio_gpio_event_vq },
        };
        struct virtqueue *vqs[2] = { NULL, NULL };
        int ret;

        ret = virtio_find_vqs(vdev, vgpio->irq_lines ? 2 : 1, vqs,
                              vqs_info, 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");
                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,
                                          u32 gpio_names_size, u16 ngpio)
{
        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 (!gpio_names_size)
                return NULL;

        len = sizeof(*res) + 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, ngpio, sizeof(*names), GFP_KERNEL);
        if (!names)
                return NULL;

        /* NULL terminate the string instead of checking it */
        gpio_names[gpio_names_size - 1] = '\0';

        for (i = 0, str = gpio_names; i < ngpio; i++) {
                names[i] = str;
                str += strlen(str) + 1; /* zero-length strings are allowed */

                if (str > gpio_names + 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 device *dev = &vdev->dev;
        struct virtio_gpio *vgpio;
        struct irq_chip *gpio_irq_chip;
        u32 gpio_names_size;
        u16 ngpio;
        int ret, i;

        vgpio = devm_kzalloc(dev, sizeof(*vgpio), GFP_KERNEL);
        if (!vgpio)
                return -ENOMEM;

        /* Read configuration */
        gpio_names_size =
                virtio_cread32(vdev, offsetof(struct virtio_gpio_config,
                                              gpio_names_size));
        ngpio =  virtio_cread16(vdev, offsetof(struct virtio_gpio_config,
                                               ngpio));
        if (!ngpio) {
                dev_err(dev, "Number of GPIOs can't be zero\n");
                return -EINVAL;
        }

        vgpio->lines = devm_kcalloc(dev, ngpio, sizeof(*vgpio->lines), GFP_KERNEL);
        if (!vgpio->lines)
                return -ENOMEM;

        for (i = 0; i < 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                 = 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;

        /* Interrupt support */
        if (virtio_has_feature(vdev, VIRTIO_GPIO_F_IRQ)) {
                vgpio->irq_lines = devm_kcalloc(dev, ngpio, sizeof(*vgpio->irq_lines), GFP_KERNEL);
                if (!vgpio->irq_lines)
                        return -ENOMEM;

                gpio_irq_chip = devm_kzalloc(dev, sizeof(*gpio_irq_chip), GFP_KERNEL);
                if (!gpio_irq_chip)
                        return -ENOMEM;

                gpio_irq_chip->name = dev_name(dev);
                gpio_irq_chip->irq_enable = virtio_gpio_irq_enable;
                gpio_irq_chip->irq_disable = virtio_gpio_irq_disable;
                gpio_irq_chip->irq_mask = virtio_gpio_irq_mask;
                gpio_irq_chip->irq_unmask = virtio_gpio_irq_unmask;
                gpio_irq_chip->irq_set_type = virtio_gpio_irq_set_type;
                gpio_irq_chip->irq_bus_lock = virtio_gpio_irq_bus_lock;
                gpio_irq_chip->irq_bus_sync_unlock = virtio_gpio_irq_bus_sync_unlock;

                /* 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              = gpio_irq_chip;

                for (i = 0; i < 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);
                raw_spin_lock_init(&vgpio->eventq_lock);
        }

        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, gpio_names_size, ngpio);

        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 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,
        .driver                 = {
                .name           = KBUILD_MODNAME,
        },
};
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");