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Date:   Fri, 29 May 2020 13:14:24 -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: <20200529201424.GA180211@roeck-us.net>
References: <20200529195951.GA3767@dtor-ws>
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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().

Thanks,
Guenter

> -	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