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From:   Guenter Roeck <groeck@google.com>
Date:   Fri, 29 May 2020 17:48:26 -0700
Message-ID: <CABXOdTeTHUtWyutfQ3oO7c_g=q5GrDsdKZbSe1dwLWSeNFi-sQ@mail.gmail.com>
Subject: Re: [PATCH] HID: usbhid: do not sleep when opening device
To:     Nicolas Boichat <drinkcat@chromium.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Guenter Roeck <groeck@chromium.org>, linux-usb@vger.kernel.org,
        "open list:HID CORE LAYER" <linux-input@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
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On Fri, May 29, 2020 at 4:50 PM Nicolas Boichat <drinkcat@chromium.org> wrote:
>
> On Sat, May 30, 2020 at 3:59 AM Dmitry Torokhov
> <dmitry.torokhov@gmail.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@chromium.org>
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.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@1000Hz is "only" 49.7 days...)
>

time_after() is overflow-safe. That is why it is used and jiffies is
not compared directly.

Guenter

> >                         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