From mboxrd@z Thu Jan 1 00:00:00 1970 From: Adam Jackson Subject: Re: Thinkpad T420 and single/dual channel lvds Date: Wed, 14 Mar 2012 10:45:06 -0400 Message-ID: <1331736306.30864.7.camel@atropine> References: <201203141337.14798.helge.bahmann@secunet.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1172917931==" Return-path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by gabe.freedesktop.org (Postfix) with ESMTP id 14C409E902 for ; Wed, 14 Mar 2012 07:45:13 -0700 (PDT) In-Reply-To: <201203141337.14798.helge.bahmann@secunet.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Helge Bahmann Cc: intel-gfx@lists.freedesktop.org, hcb@chaoticmind.net List-Id: intel-gfx@lists.freedesktop.org --===============1172917931== Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-BN6wdksCzzVnpneh3bdO" --=-BN6wdksCzzVnpneh3bdO Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2012-03-14 at 13:37 +0100, Helge Bahmann wrote: > Hi everyone, >=20 > Booting a Thinkpad T420 with the lid closed results and opening it subseq= uently results in an=20 > unusable picture on the panel (and no amount of resetting makes it usable= ): The even pixels show=20 > the nominal content of the framebuffer (with the right half missing) whli= e the odd pixels show a=20 > red-/blueish flicker. >=20 > A little bit of investigation revealed that with the lid closed on boot, = the panel ends up driven in=20 > lvds single channel mode, which the panel probably does not like. It appe= ars that the i915 driver=20 > relies on the BIOS setting up the PCH_LVDS register for dual channel and = will otherwise not ever=20 > consider switching. >=20 > While the following hack makes my display work, it is quite obviously not= the right thing to do --=20 > could you investigate if there is a "proper" way to determine whether the= panel is supposed to be=20 > driven dual channel? Nice find! There may or may not be a bit for this in the VBT in the BIOS. But the more reliably correct thing I suspect would be to just look at the preferred mode for the panel and assume it's dual-link LVDS if the pixel clock is >112MHz, since that's the crossover frequency. - ajax --=-BN6wdksCzzVnpneh3bdO Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEABECAAYFAk9grvIACgkQW4otUKDs0NPDKQCfQAIzCwROzu9DiFmMUBj5U63+ XzYAnApLYE6YM0gP7a5hxyHHi8n/DY/V =GE4b -----END PGP SIGNATURE----- --=-BN6wdksCzzVnpneh3bdO-- --===============1172917931== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx --===============1172917931==--