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SubjectRe: [PATCH] HID: usbhid: do not sleep when opening device
On Fri, May 29, 2020 at 01:33:24PM -0700, Dmitry Torokhov wrote:
> On Fri, May 29, 2020 at 01:14:24PM -0700, Guenter Roeck wrote:
> > On Fri, May 29, 2020 at 12:59:51PM -0700, Dmitry Torokhov 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)) {
> > > 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);
> > > -
> > Can you just set usbhid->input_start_time here ?
> > if (res == 0)
> > usbhid->input_start_time = jiffies + msecs_to_jiffies(50);
> > clear_bit(HID_RESUME_RUNNING, &usbhid->iofl);
> >
> > Then you might not need the added code in hid_start_in().
>
> That was my first version, but if hid_start_in() fails we start a timer
> and try to retry the IO (and the "res" in 0 in this case). And we want
> to mark the time only after we successfully submitted the interrupt URB,
> that is why the code is in hid_start_in().
>

Ah yes, that makes sense.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

Thanks,
Guenter

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