linux-kernel - Re: video: USB webcam fails since kernel 3.2

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Message-ID: <4FFAD8D9.8070203@redhat.com>
Date:	Mon, 09 Jul 2012 15:12:57 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	martin-eric.racine@....fi
CC:	Jean-François Moine <moinejf@...e.fr>,
	677533@...s.debian.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: video: USB webcam fails since kernel 3.2

Hi,

On 07/09/2012 01:33 PM, Martin-Éric Racine wrote:

<snip>

>> Hmm, this is then likely caused by the new isoc bandwidth negotiation code
>> in 3.2, unfortunately the vc032x driver is one of the few gspca drivers
>> for which I don't have a cam to test with. Can you try to build your own
>> kernel from source?
>>
>> Boot into your own kernel, and verify the regression is still there,
>> then edit drivers/media/video/gspca/gspca.c and go to the which_bandwidth
>> function, and at the beginning of this function add the following line:
>>
>> return 2000 * 2000 * 120;
>>
>> Then rebuild and re-install the kernel and try again.
>>
>> If that helps, remove the added
>> return 2000 * 2000 * 120;
>> line, and also remove the following lines from which_bandwidth:
>>
>>          /* if the image is compressed, estimate its mean size */
>>          if (!gspca_dev->cam.needs_full_bandwidth &&
>>              bandwidth < gspca_dev->cam.cam_mode[i].width *
>>                                  gspca_dev->cam.cam_mode[i].height)
>>                  bandwidth = bandwidth * 3 / 8;  /* 0.375 */
>>
>> And try again if things still work this way.
>>
>> Once you've tested this I can try to write a fix for this.
>
> Hans,
>
> Thank you for your reply.
>
> Just to eliminate the possibility of mistakes on my part while trying
> to perform the above changes, could you send me a patch against Linux
> 3.2.21 that I could apply as-is, before building myself a test kernel
> package?

Erm, that is quite a bit of work from my side for something which you
can easily do yourself, edit gspca.c, search for which_bandwidth
and then under the following lines:
         u32 bandwidth;
         int i;

Add a line like this:
	return 2000 * 2000 * 120;

Regards,

Hans
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