linux-kernel - Re: [PATCH] HID: usbhid: do not sleep when opening device

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Date:   Sat, 30 May 2020 07:50:13 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Guenter Roeck <groeck@...omium.org>, linux-usb@...r.kernel.org,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: usbhid: do not sleep when opening device

On Sat, May 30, 2020 at 3:59 AM Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
>
> usbhid tries to give the device 50 milliseconds to drain its queues
> when opening the device, but does 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@...omium.org>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>  drivers/hid/usbhid/hid-core.c | 27 +++++++++++++++------------
>  drivers/hid/usbhid/usbhid.h   |  1 +
>  2 files changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
> index c7bc9db5b192..e69992e945b2 100644
> --- a/drivers/hid/usbhid/hid-core.c
> +++ b/drivers/hid/usbhid/hid-core.c
> @@ -95,6 +95,19 @@ 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_and_clear_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 = jiffies +
> +                                                          msecs_to_jiffies(50);
> +                       }
>                 }
>         }
>         spin_unlock_irqrestore(&usbhid->lock, flags);
> @@ -280,7 +293,8 @@ 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)) {
> +               if (!test_bit(HID_RESUME_RUNNING, &usbhid->iofl) &&
> +                   time_after(jiffies, usbhid->input_start_time)) {

Are we worried about jiffies overflowing (32-bit@...0Hz is "only" 49.7 days...)

>                         hid_input_report(urb->context, HID_INPUT_REPORT,
>                                          urb->transfer_buffer,
>                                          urb->actual_length, 1);
> @@ -714,17 +728,6 @@ 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..805949671b96 100644
> --- a/drivers/hid/usbhid/usbhid.h
> +++ b/drivers/hid/usbhid/usbhid.h
> @@ -82,6 +82,7 @@ struct usbhid_device {
>
>         spinlock_t lock;                                                /* fifo spinlock */
>         unsigned long iofl;                                             /* I/O flags (CTRL_RUNNING, OUT_RUNNING) */
> +       unsigned long input_start_time;                                 /* When to start handling input, in jiffies */
>         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.rc0.183.gde8f92d652-goog
>
>
> --
> Dmitry