From mboxrd@z Thu Jan  1 00:00:00 1970
From: Adam Jackson <ajax@redhat.com>
Subject: Re: [PATCH] drm/i915: always set FDI composite sync bit
Date: Tue, 11 Oct 2011 12:42:22 -0400
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On 10/11/11 12:16 PM, Jesse Barnes wrote:
> On Tue, 11 Oct 2011 10:10:24 -0400 Adam Jackson<ajax@redhat.com>  wrote:
>> It still seems entirely magical and probably wrong in some situations.
>> And I'm thrilled to see that PPT is functionally different from CPT
>> (seriously, stop doing that) instead of just moving bit definitions
>> around (seriously, stop doing that).  But this change is massively
>> better than before.
>
> Without composite sync, FDI needs frame/line sync (the fsync/lsync
> mentioned in the docs), which means extra wires between the CPU and
> PCH.  Some boards don't have these and so we need to use composite.
> For the same reason, if FDI B and C are sharing lanes, we need to use
> composite or we won't have enough lines to go around.
>
> I've asked the hardware guys whether using composite on a board that
> supports fsync/lsync is ok generally; if so just defaulting to that
> everywhere should be fine.

Makes sense.  If true this seems worth doing for CPT too.  The IBX docs 
don't make any mention of composite sync.

- ajax