Re: [PATCH] usb: Increase quirk delay for USB devices

From: Dmitry Fleytman <dmitry@daynix.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	Samuel Thibault <samuel.thibault@ens-lyon.org>,
	Mathias Nyman <mathias.nyman@linux.intel.com>,
	Johan Hovold <johan@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Eugene Korenevsky <ekorenevsky@gmail.com>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: Increase quirk delay for USB devices
Date: Wed, 6 Sep 2017 15:34:02 +0300	[thread overview]
Message-ID: <FF810319-E7F4-403F-ABAD-07C4348B0D75@daynix.com> (raw)
In-Reply-To: <20170905202225.GC16996@roeck-us.net>

> On 5 Sep 2017, at 23:22 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> 
> On Tue, Sep 05, 2017 at 11:40:56AM +0300, Dmitry Fleytman wrote:
>> Commit e0429362ab15
>> ("usb: Add device quirk for Logitech HD Pro Webcams C920 and C930e")
>> introduced quirk to workaround an issue with some Logitech webcams.
>> 
>> The workaround is introducing delay for some USB operations.
>> 
>> According to our testing, delay introduced by original commit
>> is not long enough and in rare cases we still see issues described
>> by the aforementioned commit.
>> 
>> This patch increases delays introduced by original commit.
>> Having this patch applied we do not see those problems anymore.
>> 
>> Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
>> ---
>> drivers/usb/core/config.c | 2 +-
>> drivers/usb/core/hub.c    | 2 +-
>> 2 files changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
>> index 4be52c6..854c8d6 100644
>> --- a/drivers/usb/core/config.c
>> +++ b/drivers/usb/core/config.c
>> @@ -852,7 +852,7 @@ int usb_get_configuration(struct usb_device *dev)
>> 		}
>> 
>> 		if (dev->quirks & USB_QUIRK_DELAY_INIT)
>> -			msleep(100);
>> +			msleep(200);
> 
> How did you determine the new delays ? Was it discussed with the vendor,
> or is it based on trial and error ?

It was based in trial and error.

> 
> Either case, did you confirm that you need to increase both delays
> for the problem to disappear ?

Yes, according to testing results on our setups.

Thanks,
Dmitry

> 
> Thanks,
> Guenter
> 
>> 
>> 		result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno,
>> 		    bigbuffer, length);
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index 822f8c5..78c2aca 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -4825,7 +4825,7 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>> 			goto loop;
>> 
>> 		if (udev->quirks & USB_QUIRK_DELAY_INIT)
>> -			msleep(1000);
>> +			msleep(2000);
>> 
>> 		/* consecutive bus-powered hubs aren't reliable; they can
>> 		 * violate the voltage drop budget.  if the new child has
>> -- 
>> 2.7.4