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SubjectRe: I2C regression in post 2.6.14 gits.. -- get_user_pages() is real bug..
On Fri, Nov 04, 2005 at 10:29:34AM +0100, Jean Delvare wrote:
> Hi Matti,
>
> On 2005-11-04, Matti Aarnio wrote:
> > Specifically, BTTV driver fails to control internal
> > I2C devices in Hauppauge WinTV card with Bt848 onboard.
>
> Can you detail how you came up with this diagnosis?
>
> > Baseline 2.6.14 works fine, but 2.6.14-git2 fails.
>
> Can you please try 2.6.14-git1 and 2.6.14-rc5-mm1? This should help us
> norrow the faulty patch. Also, please confirm that 2.6.14-git7 still has
> the problem.
>
> > Any ideas ? Possible fixes ?
>
> Enable as many debugging as possible, in particular I2C Core debugging
> (I2C_DEBUG_CORE=y) in a working kernel and a non-working kernel, and
> send both logs for comparison.
>
> Thanks a lot for testing, BTW.


Since then I have been tracking of what really fails in the bttv driver,
and running: strace -o tvtime.log tvtime
Result is most revealing in failures.

The fault is not in I2C, but appears in video_buf module failing
calls of get_user_pages() with -EFAULT.

There has been lots of discussion about it back in August, but apparently
only now in post 2.6.14 the changes made it into mm/memory.c which
faulted this thing for BTTV.


Oh yes, I do use Fedora Core development kernels, and don't usually
(anymore) compile things myself, but now I had a weekend off...


> --
> Jean Delvare

/Matti Aarnio
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