[Intel-gfx] [PATCH 1/4] drm/i915: Configure the TV sense state correctly on GM45 to make TV detection reliable

[Eric Anholt]

On Wed,  7 Apr 2010 17:11:19 +0800, Zhenyu Wang <zhenyuw at linux.intel.com> wrote:
> From: ykzhao <yakui.zhao at intel.com>
> 
> The TV detection logic is not reliable on the Cantiga platform.
> Sometimes the TV will be misdetected as the following two cases:
> - TV is misdetected on some laptops. e.g. There is no TV connector
> port or no TV is attached. But the TV is shown as connected.
> - TV connector type is misdetected. e.g. the component TV is
> attached, but the TV is shown as S-video type.
> 
> According to the hardware requirement, the TV sense state bits of TV DAC
> register should be cleared to zero on Cantiga platfrom.
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=14792

As far as I can tell from reading the specs, this patch just completely
breaks TV detect on GM45.  And the logic of "set all the bits for the
register setting we're going to do and then if it's gm45 skip a few of
them" is unintuitive and backwards, even if it was correct.

You don't get to just say "according to the hardware requirement."  You
need to refer to either the b-spec (so someone can confirm what you
read) or BIOS traces (so someone knows how you did it) or to a personal
conversation with a HW engineer (so people can be appropriately
dubious), or to randomly shuffling bits of the registers until people
reported that their bug was fixed, as this patch appears to do.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 197 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/intel-gfx/attachments/20100409/8ee95da0/attachment.sig>