linux-kernel - Re: [Intel-gfx] [PATCH 04/21] drm/i915: Only use VBT panel mode on eDP if no EDID is found

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20111003134250.54221856@jbarnes-desktop>
Date:	Mon, 3 Oct 2011 13:42:50 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Keith Packard <keithp@...thp.com>
Cc:	Daniel Vetter <daniel@...ll.ch>, Dave Airlie <airlied@...hat.com>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 04/21] drm/i915: Only use VBT panel mode on
 eDP if no EDID is found

On Fri, 30 Sep 2011 10:58:26 -0700
Keith Packard <keithp@...thp.com> wrote:

> On Fri, 30 Sep 2011 18:32:35 +0200, Daniel Vetter <daniel@...ll.ch> wrote:
> 
> > Ok, this is way over my head, just checked whether the patch does what it
> > claims to - nice exercise in reading dp modeset code ;-)
> 
> Yeah, it's purely heuristic -- the VBT contains a mode which was
> originally for the LVDS. It's unclear whether it should ever be applied
> to an eDP panel, but absent other information, it seems like we should
> at least consider it.
> 
> Many LVDS panels don't bother to include an EDID rom, or the vendor
> didn't bother to hook up the DDC wire; presumably it's cheaper for them
> to stick more data in the VBIOS than add hardware.  However, there are
> some LVDS panels with EDID roms which contain *incorrect* mode data for
> the panel (amazing, I know), and so the driver prefers to use the VBT
> data when both are present.
> 
> eDP, on the other hand, doesn't require any additional wiring (at least)
> to connect up the DDC channel, and eDP panels are required to provide
> EDID data. So far, in my (very small) sample set, I've got one machine
> which provides accurate VBT *and* EDID data (an HP 2540p) and one
> machine which provides inaccurate VBT data but accurate EDID data (a
> MacBook air). So, I just decided to prefer the EDID data.
> 
> One option would be to extract the current mode from the hardware when
> the driver starts and use that if present. But, that might mean that
> you'd get different modes depending on whether the machine booted with
> the lid closed or open, which seems like a bad plan.

More than that, I think eDP *requires* an EDID, and it sounds like even
the Air has one (and if any machine didn't, you know it would be an
Apple).

So I'm definitely in favor of this change.

-- 
Jesse Barnes, Intel Open Source Technology Center
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/