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Date:   Fri, 29 May 2020 13:44:50 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc:     Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        groeck@chromium.org, Nicolas Boichat <drinkcat@chromium.org>,
        linux-usb@vger.kernel.org, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] HID: usbhid: do not sleep when opening device
Message-ID: <20200529204450.GA184901@roeck-us.net>
References: <20200529195951.GA3767@dtor-ws>
 <20200529201424.GA180211@roeck-us.net>
 <20200529203324.GL89269@dtor-ws>
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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