From: Keith Packard Subject: Re: i915 SSC Patch Date: Fri, 29 Jul 2011 15:18:05 -0700 Message-ID: References: <4E32ADC7.3080002@codethink.co.uk> <201107291801.40049.gene.heskett@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha1; protocol="application/pgp-signature" Return-path: In-Reply-To: <201107291801.40049.gene.heskett@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Gene Heskett , Ben Brewer , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org List-Id: dri-devel@lists.freedesktop.org --=-=-= Content-Transfer-Encoding: quoted-printable On Fri, 29 Jul 2011 18:01:39 -0400, Gene Heskett w= rote: > On Friday, July 29, 2011, Keith Packard wrote: > >On Fri, 29 Jul 2011 13:55:35 +0100, Ben Brewer=20 > wrote: > >> I've added a global SSC (Spread Spectrum Clock) parameter to the i915 > >> driver, since having SSC enabled breaks (distorts) VGA output on some > >> Core i5/i7 chips (see > >> https://bugs.freedesktop.org/show_bug.cgi?id=3D38750). SSC is still > >> enabled by default so the behaviour won't change but setting the > >> global_use_ssc parameter will turn this feature off and allow affected > >> devices to function correctly (notably the Dell Vostro 3300). > > > >The question I have is why is SSC enabled on the VGA output at all? I > >don't see any way VGA could ever tolerate it. >=20 > Something does not make sense here Keith, so I'm with you, and my=20 > background is from about 60 years in tv maintenance and 45 in > broadcasting. Right, I think the basic problem is that we aren't switching SSC on and off based on whether there's an output which can't tolerate it. Making this user-configurable doesn't make any sense, it clearly needs to be done in the driver automatically, based on whether there's an analog output running (VGA or TV). > Hardware design error in the Dell? Nope, just a driver bug :-) =2D-=20 keith.packard@intel.com --=-=-= Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iD8DBQFOMzGdQp8BWwlsTdMRAkNnAJ0U6QuuCzakC8t/3qyUnFrfX+s21QCgtGru 5cBVQmwNoouZW1hlUmJWfWw= =xApM -----END PGP SIGNATURE----- --=-=-=--