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Message-ID: <CAMpxmJVeAKpNnX0HXSNSLYqX6T+qxun8ppZ7EwzFb3WsS=nanw@mail.gmail.com>
Date: Sun, 16 Aug 2020 16:32:34 +0200
From: Bartosz Golaszewski <bgolaszewski@...libre.com>
To: Kent Gibson <warthog618@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
linux-gpio <linux-gpio@...r.kernel.org>,
Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v4 09/20] gpiolib: cdev: support edge detection for uAPI v2
On Fri, Aug 14, 2020 at 5:04 AM Kent Gibson <warthog618@...il.com> wrote:
>
> Add support for edge detection to lines requested using
> GPIO_V2_GET_LINE_IOCTL.
>
> Signed-off-by: Kent Gibson <warthog618@...il.com>
> ---
>
> The edge_detector implementation is based on the v1 lineevent implementation.
>
> drivers/gpio/gpiolib-cdev.c | 316 +++++++++++++++++++++++++++++++++++-
> drivers/gpio/gpiolib.c | 2 +
> drivers/gpio/gpiolib.h | 2 +
> 3 files changed, 319 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index 28273f3105d3..1d42a01f5414 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -382,11 +382,43 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
> }
> #endif /* CONFIG_GPIO_CDEV_V1 */
>
> +/**
> + * struct edge_detector - contains the state of a line edge detector
> + * @line: the corresponding line request
> + * @irq: the interrupt triggered in response to events on this GPIO
> + * @flags: the flags, GPIO_V2_LINE_FLAG_EDGE_RISING and/or
> + * GPIO_V2_LINE_FLAG_EDGE_FALLING, indicating the edge detection applied
> + * @timestamp: cache for the timestamp storing it between hardirq and IRQ
> + * thread, used to bring the timestamp close to the actual event
> + * @seqno: the seqno for the current edge event in the sequence of events
> + * for the corresponding line request. Ths is drawn from the @line.
> + * @line_seqno: the seqno for the current edge event in the sequence of
> + * events for this line.
> + */
> +struct edge_detector {
> + struct line *line;
> + unsigned int irq;
> + u64 flags;
> + /*
> + * timestamp and seqno are shared by edge_irq_handler() and
> + * edge_irq_thread() which are themselves mutually exclusive.
> + */
> + u64 timestamp;
> + u32 seqno;
> + u32 line_seqno;
> +};
> +
> /**
> * struct line - contains the state of a userspace line request
> * @gdev: the GPIO device the line request pertains to
> * @label: consumer label used to tag descriptors
> * @num_descs: the number of descriptors held in the descs array
> + * @wait: wait queue that handles blocking reads of events
> + * @events: KFIFO for the GPIO events
> + * @seqno: the sequence number for edge events generated on all lines in
> + * this line request. Note that this is not used when @num_descs is 1, as
> + * the line_seqno is then the same and is cheaper to calculate.
> + * @edets: an array of edge detectors, of size @num_descs
> * @descs: the GPIO descriptors held by this line request, with @num_descs
> * elements.
> */
> @@ -394,9 +426,146 @@ struct line {
> struct gpio_device *gdev;
> const char *label;
> u32 num_descs;
> + wait_queue_head_t wait;
> + DECLARE_KFIFO_PTR(events, struct gpio_v2_line_event);
> + atomic_t seqno;
> + struct edge_detector *edets;
> struct gpio_desc *descs[];
> };
>
> +static inline struct gpio_desc *edge_detector_desc(
> + const struct edge_detector *edet)
> +{
> + return edet->line->descs[edet - &edet->line->edets[0]];
> +}
> +
> +static irqreturn_t edge_irq_thread(int irq, void *p)
> +{
> + struct edge_detector *edet = p;
> + struct line *line = edet->line;
> + struct gpio_desc *desc = edge_detector_desc(edet);
> + struct gpio_v2_line_event le;
> + int ret;
> +
> + /* Do not leak kernel stack to userspace */
> + memset(&le, 0, sizeof(le));
> +
> + /*
> + * We may be running from a nested threaded interrupt in which case
> + * we didn't get the timestamp from edge_irq_handler().
> + */
> + if (!edet->timestamp) {
> + le.timestamp = ktime_get_ns();
> + if (line->num_descs != 1)
> + edet->seqno = atomic_inc_return(&line->seqno);
> + } else {
> + le.timestamp = edet->timestamp;
> + }
> + edet->timestamp = 0;
> +
> + if (edet->flags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
> + GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
> + int level = gpiod_get_value_cansleep(desc);
> +
> + if (level)
> + /* Emit low-to-high event */
> + le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
> + else
> + /* Emit high-to-low event */
> + le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
> + } else if (edet->flags == GPIO_V2_LINE_FLAG_EDGE_RISING) {
> + /* Emit low-to-high event */
> + le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
> + } else if (edet->flags == GPIO_V2_LINE_FLAG_EDGE_FALLING) {
> + /* Emit high-to-low event */
> + le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
> + } else {
> + return IRQ_NONE;
> + }
> + edet->line_seqno++;
> + le.line_seqno = edet->line_seqno;
> + le.seqno = (line->num_descs == 1) ? le.line_seqno : edet->seqno;
> + le.offset = gpio_chip_hwgpio(desc);
> +
> + ret = kfifo_in_spinlocked_noirqsave(&line->events, &le,
> + 1, &line->wait.lock);
> + if (ret)
> + wake_up_poll(&line->wait, EPOLLIN);
> + else
> + pr_debug_ratelimited("event FIFO is full - event dropped\n");
> +
> + return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t edge_irq_handler(int irq, void *p)
> +{
> + struct edge_detector *edet = p;
> + struct line *line = edet->line;
> +
> + /*
> + * Just store the timestamp in hardirq context so we get it as
> + * close in time as possible to the actual event.
> + */
> + edet->timestamp = ktime_get_ns();
> +
> + if (line->num_descs != 1)
> + edet->seqno = atomic_inc_return(&line->seqno);
> +
> + return IRQ_WAKE_THREAD;
> +}
> +
> +static int edge_detector_start(struct edge_detector *edet)
> +{
> + int ret, irq, irqflags = 0;
> + struct gpio_desc *desc;
> +
> + desc = edge_detector_desc(edet);
> + irq = gpiod_to_irq(desc);
> +
> + if (irq <= 0)
> + return -ENODEV;
> +
> + edet->seqno = 0;
> + edet->line_seqno = 0;
> +
> + if (edet->flags & GPIO_V2_LINE_FLAG_EDGE_RISING)
> + irqflags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
> + IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;
> + if (edet->flags & GPIO_V2_LINE_FLAG_EDGE_FALLING)
> + irqflags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
> + IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
> + irqflags |= IRQF_ONESHOT;
> +
> + /* Request a thread to read the events */
> + ret = request_threaded_irq(irq,
> + edge_irq_handler,
> + edge_irq_thread,
> + irqflags,
> + edet->line->label,
> + edet);
> + if (ret)
> + return ret;
> +
> + edet->irq = irq;
> + return 0;
> +}
> +
> +static void edge_detector_stop(struct edge_detector *edet)
> +{
> + if (edet->irq) {
> + free_irq(edet->irq, edet);
> + edet->irq = 0;
> + }
> +}
> +
> +static int edge_detector_setup(struct edge_detector *edet,
> + struct gpio_v2_line_config *lc)
> +{
> + if (edet->flags)
> + return edge_detector_start(edet);
> + return 0;
> +}
> +
> #define GPIO_V2_LINE_BIAS_FLAGS \
> (GPIO_V2_LINE_FLAG_BIAS_PULL_UP | \
> GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN | \
> @@ -410,10 +579,15 @@ struct line {
> (GPIO_V2_LINE_FLAG_OPEN_DRAIN | \
> GPIO_V2_LINE_FLAG_OPEN_SOURCE)
>
> +#define GPIO_V2_LINE_EDGE_FLAGS \
> + (GPIO_V2_LINE_FLAG_EDGE_RISING | \
> + GPIO_V2_LINE_FLAG_EDGE_FALLING)
> +
> #define GPIO_V2_LINE_VALID_FLAGS \
> (GPIO_V2_LINE_FLAG_ACTIVE_LOW | \
> GPIO_V2_LINE_DIRECTION_FLAGS | \
> GPIO_V2_LINE_DRIVE_FLAGS | \
> + GPIO_V2_LINE_EDGE_FLAGS | \
> GPIO_V2_LINE_BIAS_FLAGS)
>
> static u64 gpio_v2_line_config_flags(struct gpio_v2_line_config *lc,
> @@ -430,6 +604,21 @@ static u64 gpio_v2_line_config_flags(struct gpio_v2_line_config *lc,
> return lc->flags;
> }
>
> +static int gpio_v2_line_config_has_edge_detection(struct gpio_v2_line_config *lc)
> +{
> + int i;
> +
> + if (lc->flags & GPIO_V2_LINE_EDGE_FLAGS)
> + return 1;
> +
> + for (i = 0; i < lc->num_attrs; i--) {
> + if ((lc->attrs[i].attr.id == GPIO_V2_LINE_ATTR_ID_FLAGS) &&
> + (lc->attrs[i].attr.flags & GPIO_V2_LINE_EDGE_FLAGS))
> + return 1;
> + }
> + return 0;
> +}
> +
> static int gpio_v2_line_config_output_value(struct gpio_v2_line_config *lc,
> int line_idx)
> {
> @@ -458,6 +647,11 @@ static int gpio_v2_line_flags_validate(u64 flags)
> (flags & GPIO_V2_LINE_FLAG_OUTPUT))
> return -EINVAL;
>
> + /* Edge detection requires explicit input. */
> + if ((flags & GPIO_V2_LINE_EDGE_FLAGS) &&
> + !(flags & GPIO_V2_LINE_FLAG_INPUT))
> + return -EINVAL;
> +
> /*
> * Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
> * the hardware actually supports enabling both at the same time the
> @@ -518,6 +712,10 @@ static void gpio_v2_line_config_flags_to_desc_flags(u64 flags,
> set_bit(FLAG_IS_OUT, flagsp);
> else if (flags & GPIO_V2_LINE_FLAG_INPUT)
> clear_bit(FLAG_IS_OUT, flagsp);
> + assign_bit(FLAG_EDGE_RISING, flagsp,
> + flags & GPIO_V2_LINE_FLAG_EDGE_RISING);
> + assign_bit(FLAG_EDGE_FALLING, flagsp,
> + flags & GPIO_V2_LINE_FLAG_EDGE_FALLING);
> assign_bit(FLAG_OPEN_DRAIN, flagsp,
> flags & GPIO_V2_LINE_FLAG_OPEN_DRAIN);
> assign_bit(FLAG_OPEN_SOURCE, flagsp,
> @@ -605,14 +803,87 @@ static long line_ioctl_compat(struct file *file, unsigned int cmd,
> }
> #endif
>
> +static __poll_t line_poll(struct file *file,
> + struct poll_table_struct *wait)
> +{
> + struct line *line = file->private_data;
> + __poll_t events = 0;
> +
> + poll_wait(file, &line->wait, wait);
> +
> + if (!kfifo_is_empty_spinlocked_noirqsave(&line->events,
> + &line->wait.lock))
> + events = EPOLLIN | EPOLLRDNORM;
> +
> + return events;
> +}
> +
> +static ssize_t line_read(struct file *file,
> + char __user *buf,
> + size_t count,
> + loff_t *f_ps)
> +{
> + struct line *line = file->private_data;
> + struct gpio_v2_line_event le;
> + ssize_t bytes_read = 0;
> + int ret;
> +
> + if (count < sizeof(le))
> + return -EINVAL;
> +
> + do {
> + spin_lock(&line->wait.lock);
> + if (kfifo_is_empty(&line->events)) {
> + if (bytes_read) {
> + spin_unlock(&line->wait.lock);
> + return bytes_read;
> + }
> +
> + if (file->f_flags & O_NONBLOCK) {
> + spin_unlock(&line->wait.lock);
> + return -EAGAIN;
> + }
> +
> + ret = wait_event_interruptible_locked(line->wait,
> + !kfifo_is_empty(&line->events));
> + if (ret) {
> + spin_unlock(&line->wait.lock);
> + return ret;
> + }
> + }
> +
> + ret = kfifo_out(&line->events, &le, 1);
> + spin_unlock(&line->wait.lock);
> + if (ret != 1) {
> + /*
> + * This should never happen - we were holding the
> + * lock from the moment we learned the fifo is no
> + * longer empty until now.
> + */
> + ret = -EIO;
> + break;
> + }
> +
> + if (copy_to_user(buf + bytes_read, &le, sizeof(le)))
> + return -EFAULT;
> + bytes_read += sizeof(le);
> + } while (count >= bytes_read + sizeof(le));
> +
> + return bytes_read;
> +}
> +
> static void line_free(struct line *line)
> {
> int i;
>
> for (i = 0; i < line->num_descs; i++) {
> + if (line->edets)
> + edge_detector_stop(&line->edets[i]);
> if (line->descs[i])
> gpiod_free(line->descs[i]);
> }
> + kfifo_free(&line->events);
> + kfree(line->edets);
> kfree(line->label);
> put_device(&line->gdev->dev);
> kfree(line);
> @@ -628,6 +899,8 @@ static int line_release(struct inode *inode, struct file *file)
>
> static const struct file_operations line_fileops = {
> .release = line_release,
> + .read = line_read,
> + .poll = line_poll,
> .owner = THIS_MODULE,
> .llseek = noop_llseek,
> .unlocked_ioctl = line_ioctl,
> @@ -641,7 +914,7 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
> struct gpio_v2_line_request lr;
> struct line *line;
> struct file *file;
> - int fd, i, ret;
> + int fd, i, ret, size, has_edge_detection;
> struct gpio_v2_line_config *lc;
> unsigned long flags;
>
> @@ -658,6 +931,11 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
> if (ret)
> return ret;
>
> + /* event_buffer_size only valid with edge detection */
> + has_edge_detection = gpio_v2_line_config_has_edge_detection(lc);
> + if (lr.event_buffer_size && !has_edge_detection)
> + return -EINVAL;
> +
> line = kzalloc(struct_size(line, descs, lr.num_lines),
> GFP_KERNEL);
> if (!line)
> @@ -666,6 +944,16 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
> line->gdev = gdev;
> get_device(&gdev->dev);
>
> + line->edets = kcalloc(lr.num_lines, sizeof(*line->edets),
> + GFP_KERNEL);
You're allocating num_lines of edge detectors even if only certain
lines have edge detection (via attributes). I don't like it but it
made me think about struct line. How about having struct line which
actually only represents a single line (and it contains the relevant
gpio_desc pointer as well as the associated edge detector and any
other data only relevant for this line) and a set of lines would be
aggregated in struct line_request or line_request_data which would
additionally contain common fields? Does that even make sense?
Bart
> + if (!line->edets) {
> + ret = -ENOMEM;
> + goto out_free_line;
> + }
> +
> + for (i = 0; i < lr.num_lines; i++)
> + line->edets[i].line = line;
> +
> /* Make sure this is terminated */
> lr.consumer[sizeof(lr.consumer)-1] = '\0';
> if (strlen(lr.consumer)) {
> @@ -676,6 +964,21 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
> }
> }
>
> + init_waitqueue_head(&line->wait);
> + if (has_edge_detection) {
> + size = lr.event_buffer_size;
> +
> + if (size > GPIO_V2_LINES_MAX*16)
> + size = GPIO_V2_LINES_MAX*16;
> + else if (size == 0)
> + size = lr.num_lines*16;
> +
> + ret = kfifo_alloc(&line->events, size, GFP_KERNEL);
> + if (ret)
> + goto out_free_line;
> + }
> +
> + atomic_set(&line->seqno, 0);
> line->num_descs = lr.num_lines;
>
> /* Request each GPIO */
> @@ -714,6 +1017,10 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
> ret = gpiod_direction_input(desc);
> if (ret)
> goto out_free_line;
> + line->edets[i].flags = flags & GPIO_V2_LINE_EDGE_FLAGS;
> + ret = edge_detector_setup(&line->edets[i], lc);
> + if (ret)
> + goto out_free_line;
> }
>
> blocking_notifier_call_chain(&desc->gdev->notifier,
> @@ -1237,6 +1544,13 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
> if (test_bit(FLAG_PULL_UP, &desc->flags))
> info->flags |= GPIO_V2_LINE_FLAG_BIAS_PULL_UP;
>
> + if (test_bit(FLAG_EDGE_RISING, &desc->flags))
> + info->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
> + if (test_bit(FLAG_EDGE_FALLING, &desc->flags))
> + info->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;
> +
> + info->num_attrs = 0;
> +
> spin_unlock_irqrestore(&gpio_lock, flags);
> }
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 80137c1b3cdc..e4c81dca7f8b 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2041,6 +2041,8 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
> clear_bit(FLAG_PULL_UP, &desc->flags);
> clear_bit(FLAG_PULL_DOWN, &desc->flags);
> clear_bit(FLAG_BIAS_DISABLE, &desc->flags);
> + clear_bit(FLAG_EDGE_RISING, &desc->flags);
> + clear_bit(FLAG_EDGE_FALLING, &desc->flags);
> clear_bit(FLAG_IS_HOGGED, &desc->flags);
> #ifdef CONFIG_OF_DYNAMIC
> desc->hog = NULL;
> diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
> index 6709f79c02dd..39b356160937 100644
> --- a/drivers/gpio/gpiolib.h
> +++ b/drivers/gpio/gpiolib.h
> @@ -114,6 +114,8 @@ struct gpio_desc {
> #define FLAG_PULL_UP 13 /* GPIO has pull up enabled */
> #define FLAG_PULL_DOWN 14 /* GPIO has pull down enabled */
> #define FLAG_BIAS_DISABLE 15 /* GPIO has pull disabled */
> +#define FLAG_EDGE_RISING 16 /* GPIO CDEV detects rising edge events */
> +#define FLAG_EDGE_FALLING 17 /* GPIO CDEV detects falling edge events */
>
> /* Connection label */
> const char *label;
> --
> 2.28.0
>
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