On Fri, May 29, 2020 at 4:50 PM Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote:
>
> On Sat, May 30, 2020 at 3:59 AM Dmitry Torokhov
> <dmitry.torokhov@xxxxxxxxx> 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@xxxxxxxxxxxx>
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> > ---
> > 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
