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Date: Mon, 09 Jul 2012 15:12:57 +0200
From: Hans de Goede <hdegoede@redhat.com>
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To: martin-eric.racine@iki.fi
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Subject: Re: video: USB webcam fails since kernel 3.2
References: <20120614162609.4613.22122.reportbug@henna.lan> <20120614215359.GF3537@burratino> <CAPZXPQd9gNCxn7xGyqj_xymPaF5OxvRtxRFkt+SsLs942te4og@mail.gmail.com> <20120616044137.GB4076@burratino> <1339932233.20497.14.camel@henna.lan> <CAPZXPQegp7RA5M0H9Ofq4rJ9aj-rEdg=Ly9_1c6vAKi3COw50g@mail.gmail.com> <4FF9CA30.9050105@redhat.com> <CAPZXPQd026xfKrAU0D7CLQGbdAs8U01u5vsHp+5-wbVofAwdqQ@mail.gmail.com>
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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