Re: [PATCH v2] HID: usbhid: do not sleep when opening device

[Guenter Roeck <groeck@google.com>]

On Tue, Jun 9, 2020 at 9:38 PM Dmitry Torokhov
<dmitry.torokhov@gmail.com> wrote:
>
> usbhid tries to give the device 50 milliseconds to drain its queues when
> opening the device, but dies it naively by simply sleeping in open handler,
> which slows down device probing (and thus may affect overall boot time).
>
> However we do not need to sleep as we can instead mark a point of time in
> the future when we should start processing the events.
>
> Reported-by: Nicolas Boichat <drinkcat@chromium.org>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Reviewed-by: Guenter Roeck <groeck@chromium.org>

> ---
>
> v2: switched from using jiffies to ktime_t to make sure we won't have
> issues with jiffies overflowing.
>
>  drivers/hid/usbhid/hid-core.c | 53 +++++++++++++++++++----------------
>  drivers/hid/usbhid/usbhid.h   |  2 ++
>  2 files changed, 31 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
> index c7bc9db5b192..72c92aab2b18 100644
> --- a/drivers/hid/usbhid/hid-core.c
> +++ b/drivers/hid/usbhid/hid-core.c
> @@ -26,6 +26,7 @@
>  #include <linux/wait.h>
>  #include <linux/workqueue.h>
>  #include <linux/string.h>
> +#include <linux/timekeeping.h>
>
>  #include <linux/usb.h>
>
> @@ -95,6 +96,18 @@ static int hid_start_in(struct hid_device *hid)
>                                 set_bit(HID_NO_BANDWIDTH, &usbhid->iofl);
>                 } else {
>                         clear_bit(HID_NO_BANDWIDTH, &usbhid->iofl);
> +
> +                       if (test_bit(HID_RESUME_RUNNING, &usbhid->iofl)) {
> +                               /*
> +                                * In case events are generated while nobody was
> +                                * listening, some are released when the device
> +                                * is re-opened. Wait 50 msec for the queue to
> +                                * empty before allowing events to go through
> +                                * hid.
> +                                */
> +                               usbhid->input_start_time =
> +                                       ktime_add_ms(ktime_get_coarse(), 50);
> +                       }
>                 }
>         }
>         spin_unlock_irqrestore(&usbhid->lock, flags);
> @@ -280,20 +293,23 @@ static void hid_irq_in(struct urb *urb)
>                 if (!test_bit(HID_OPENED, &usbhid->iofl))
>                         break;
>                 usbhid_mark_busy(usbhid);
> -               if (!test_bit(HID_RESUME_RUNNING, &usbhid->iofl)) {
> -                       hid_input_report(urb->context, HID_INPUT_REPORT,
> -                                        urb->transfer_buffer,
> -                                        urb->actual_length, 1);
> -                       /*
> -                        * autosuspend refused while keys are pressed
> -                        * because most keyboards don't wake up when
> -                        * a key is released
> -                        */
> -                       if (hid_check_keys_pressed(hid))
> -                               set_bit(HID_KEYS_PRESSED, &usbhid->iofl);
> -                       else
> -                               clear_bit(HID_KEYS_PRESSED, &usbhid->iofl);
> +               if (test_bit(HID_RESUME_RUNNING, &usbhid->iofl)) {
> +                       if (ktime_before(ktime_get_coarse(),
> +                                        usbhid->input_start_time))
> +                               break;
> +                       clear_bit(HID_RESUME_RUNNING, &usbhid->iofl);
>                 }
> +               hid_input_report(urb->context, HID_INPUT_REPORT,
> +                                urb->transfer_buffer, urb->actual_length, 1);
> +               /*
> +                * autosuspend refused while keys are pressed
> +                * because most keyboards don't wake up when
> +                * a key is released
> +                */
> +               if (hid_check_keys_pressed(hid))
> +                       set_bit(HID_KEYS_PRESSED, &usbhid->iofl);
> +               else
> +                       clear_bit(HID_KEYS_PRESSED, &usbhid->iofl);
>                 break;
>         case -EPIPE:            /* stall */
>                 usbhid_mark_busy(usbhid);
> @@ -714,17 +730,6 @@ static int usbhid_open(struct hid_device *hid)
>         }
>
>         usb_autopm_put_interface(usbhid->intf);
> -
> -       /*
> -        * In case events are generated while nobody was listening,
> -        * some are released when the device is re-opened.
> -        * Wait 50 msec for the queue to empty before allowing events
> -        * to go through hid.
> -        */
> -       if (res == 0)
> -               msleep(50);
> -
> -       clear_bit(HID_RESUME_RUNNING, &usbhid->iofl);
>         return res;
>  }
>
> diff --git a/drivers/hid/usbhid/usbhid.h b/drivers/hid/usbhid/usbhid.h
> index 8620408bd7af..0f0bcf7037f8 100644
> --- a/drivers/hid/usbhid/usbhid.h
> +++ b/drivers/hid/usbhid/usbhid.h
> @@ -13,6 +13,7 @@
>
>  #include <linux/types.h>
>  #include <linux/slab.h>
> +#include <linux/ktime.h>
>  #include <linux/list.h>
>  #include <linux/mutex.h>
>  #include <linux/timer.h>
> @@ -82,6 +83,7 @@ struct usbhid_device {
>
>         spinlock_t lock;                                                /* fifo spinlock */
>         unsigned long iofl;                                             /* I/O flags (CTRL_RUNNING, OUT_RUNNING) */
> +       ktime_t input_start_time;                                       /* When to start handling input */
>         struct timer_list io_retry;                                     /* Retry timer */
>         unsigned long stop_retry;                                       /* Time to give up, in jiffies */
>         unsigned int retry_delay;                                       /* Delay length in ms */
> --
> 2.27.0.278.ge193c7cf3a9-goog
>
>
> --
> Dmitry