Re: [RFC PATCH v1 11/20] gpio: Add event count interface to gpiolib

[Bartosz Golaszewski]

On Tue, Aug 24, 2021 at 6:48 PM <lakshmi.sowjanya.d@xxxxxxxxx> wrote:
>
> From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
>
> Add a flag for event count and an extended structure to capture the event
> count when the flag is enabled.
>
> Intel(R) PMC Timed I/O device has an event count register counting
> the number of missed input edges. The register interface captures the
> event count and timestamp of the last event. For an event rate
> exceeding the rate that software can read events, the software can use
> the missed event count to calculate average event rates.
>
> The application requests one or both rising and falling edges when
> initializing the interface. The count of the selected edge type is
> optionally selected with an added event type flag. The event count is
> returned in an extended buffer using the read() interface.
>
> Co-developed-by: Christopher Hall <christopher.s.hall@xxxxxxxxx>
> Signed-off-by: Christopher Hall <christopher.s.hall@xxxxxxxxx>
> Signed-off-by: Tamal Saha <tamal.saha@xxxxxxxxx>
> Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
> Reviewed-by: Mark Gross <mgross@xxxxxxxxxxxxxxx>
> ---
>  drivers/gpio/gpiolib-cdev.c | 28 +++++++++++++++++++---------
>  include/linux/gpio/driver.h |  1 +
>  include/uapi/linux/gpio.h   | 12 ++++++++++++
>  3 files changed, 32 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index 1df28a71f88b..3b5719d5e2dc 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -518,7 +518,8 @@ struct linereq {
>          GPIO_V2_LINE_DRIVE_FLAGS | \
>          GPIO_V2_LINE_EDGE_FLAGS | \
>          GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME | \
> -        GPIO_V2_LINE_BIAS_FLAGS)
> +        GPIO_V2_LINE_BIAS_FLAGS | \
> +        GPIO_V2_LINE_FLAG_EVENT_COUNT)
>
>  static void linereq_put_event(struct linereq *lr,
>                               struct gpio_v2_line_event *le)
> @@ -1252,10 +1253,14 @@ static ssize_t linereq_read(struct file *file,
>         struct linereq *lr = file->private_data;
>         struct gpioevent_poll_data poll_data;
>         struct gpio_v2_line_event le;
> +       size_t min_userbuf_size;
>         ssize_t bytes_read = 0;
>         int ret, offset;
>
> -       if (count < sizeof(le))
> +       min_userbuf_size = sizeof(le);
> +       min_userbuf_size += lr->lines[0].eflags & GPIO_V2_LINE_FLAG_EVENT_COUNT ?
> +                                       sizeof(struct gpio_v2_line_event_ext) : 0;
> +       if (count < min_userbuf_size)
>                 return -EINVAL;
>
>         /* Without an IRQ, we can only poll */
> @@ -1270,12 +1275,17 @@ static ssize_t linereq_read(struct file *file,
>                                               lr->lines[offset].eflags, &poll_data);
>                 if (ret)
>                         return ret;
> -               event = kzalloc(sizeof(*event), GFP_KERNEL);
> +               event = kzalloc(min_userbuf_size, GFP_KERNEL);
>                 event->timestamp_ns = poll_data.timestamp;
>                 event->id = poll_data.id;
> -               if (copy_to_user(buf, (void *)&event, sizeof(event)))
> -                       return -EFAULT;
> -               return sizeof(event);
> +               if (lr->lines[offset].eflags & GPIO_V2_LINE_FLAG_EVENT_COUNT)
> +                       event->ext[0].event_count = poll_data.event_count;
> +
> +               ret = copy_to_user(buf, (void *)event, min_userbuf_size);
> +               if (ret)
> +                       ret = -EFAULT;
> +               kfree(event);
> +               return ret ? ret : min_userbuf_size;
>         }
>
>         do {
> @@ -1396,7 +1406,7 @@ static int setup_input(struct linereq *lr, struct gpio_v2_line_config *lc,
>         ret = edge_detector_setup(&lr->lines[line_no], lc, line_no,
>                                   lflags & GPIO_V2_LINE_EDGE_FLAGS);
>         if (ret < 0) {
> -               if (ret != -ENXIO) {
> +               if (ret == -ENXIO) {
>                         if (lr->gdev->chip->setup_poll &&
>                             lr->gdev->chip->setup_poll(lr->gdev->chip, offset,
>                                                        &lflags) == 0 &&
> @@ -1513,7 +1523,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
>                                 goto out_free_linereq;
>                 }
>
> -               file_flags = O_RDONLY | O_CLOEXEC;
> +               file_flags = O_CLOEXEC;
>                 file_flags |= output ? O_WRONLY : O_RDONLY;
>                 file_flags |= (!output && !lr->lines[i].irq) ? O_NONBLOCK : 0;
>
> @@ -1524,7 +1534,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
>                         offset);
>         }
>
> -       fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC);
> +       fd = get_unused_fd_flags(file_flags);
>         if (fd < 0) {
>                 ret = fd;
>                 goto out_free_linereq;
> diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
> index 561e289434aa..09637fcbfd52 100644
> --- a/include/linux/gpio/driver.h
> +++ b/include/linux/gpio/driver.h
> @@ -493,6 +493,7 @@ struct gpio_chip {
>  struct gpioevent_poll_data {
>         __u64 timestamp;
>         __u32 id;
> +       __u32 event_count;
>  };
>
>  struct gpio_output_event_data {
> diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
> index c39efc459b9f..e7fff2a205ec 100644
> --- a/include/uapi/linux/gpio.h
> +++ b/include/uapi/linux/gpio.h
> @@ -80,6 +80,7 @@ enum gpio_v2_line_flag {
>         GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN        = _BITULL(9),
>         GPIO_V2_LINE_FLAG_BIAS_DISABLED         = _BITULL(10),
>         GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME  = _BITULL(11),
> +       GPIO_V2_LINE_FLAG_EVENT_COUNT           = _BITULL(12),
>  };
>
>  /**
> @@ -270,6 +271,15 @@ enum gpio_v2_line_event_id {
>         GPIO_V2_LINE_EVENT_UNKNOWN_EDGE = 3,
>  };
>
> +/**
> + * struct gpio_v2_line_event_ext - Extended gpio line event
> + * @event_count: count of events
> + */
> +struct gpio_v2_line_event_ext {
> +       __u32 event_count;
> +       __u32 reserved[3];
> +};
> +
>  /**
>   * struct gpio_v2_line_event - The actual event being pushed to userspace
>   * @timestamp_ns: best estimate of time of event occurrence, in nanoseconds.
> @@ -280,6 +290,7 @@ enum gpio_v2_line_event_id {
>   * @line_seqno: the sequence number for this event in the sequence of
>   * events on this particular line
>   * @padding: reserved for future use
> + * @gpio_v2_line_event_ext: Extended gpio line event
>   *
>   * By default the @timestamp_ns is read from %CLOCK_MONOTONIC and is
>   * intended to allow the accurate measurement of the time between events.
> @@ -296,6 +307,7 @@ struct gpio_v2_line_event {
>         __u32 line_seqno;
>         /* Space reserved for future use. */
>         __u32 padding[6];
> +       struct gpio_v2_line_event_ext ext[];

This bit is an instant NAK as it breaks the ABI.

While I understand this is a bit of a different problem than the one
handled by the seqno fields, I think you should just think about
adding a field called something like "real_seqno" for those hardware
counted sequence numbers.

Bart

>  };
>
>  /**
> --
> 2.17.1
>