linux-kernel - Re: [Intel-gfx] [PATCH 3/7] drm/i915: Treat PCH eDP like DP in most places

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Date:	Wed, 02 Nov 2011 15:36:20 -0400
From:	Adam Jackson <ajax@...hat.com>
To:	Keith Packard <keithp@...thp.com>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 3/7] drm/i915: Treat PCH eDP like DP in most
 places

On 11/2/11 1:31 PM, Keith Packard wrote:
> On Wed, 02 Nov 2011 13:13:52 -0400, Adam Jackson<ajax@...hat.com>  wrote:
>
>> Given the choice of trusting DPCD or the VBT, I'd definitely prefer
>> DPCD.
>
> Except that the DPCD is coded into the monitor while the VBT is done by
> the platform. And, it's the platform which may neglect to connect some
> of the wires.

My reasoning about this has been:

The maximum link configuration in DPCD is going to fit - and minimally 
fit - the maximum supported configuration (depth/rate/size/etc), because 
otherwise the hardware would have been more expensive to produce.

The VBT is going to be crap.

But as always, "do what the Windows driver does" seems like a good 
strategy.  Do we know?

> Any bets on how long until we find a machine that has right value in the
> VBT and the wrong one in DPCD? Or a machine with wrong values in both places?

I will happily pay $20 to the first person to find a monitor with broken 
link/lane in DPCD, on the understanding that they take it (the $20) to 
the nearest hardware store, buy a hammer, and smash the monitor. 
Preferably with the video uploaded to youtube.

- ajax
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