linux-kernel - Re: [Linux-fbdev-devel] [PATCH] atyfb: fix distorted image on PowerMacs

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Date:	Wed, 04 Feb 2009 08:06:12 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Ville Syrjälä <syrjala@....fi>
Cc:	Risto Suominen <risto.suominen@...il.com>,
	Alex Kern <alex.kern@....de>, linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net
Subject: Re: [Linux-fbdev-devel] [PATCH] atyfb: fix distorted image on
 PowerMacs

On Tue, 2009-02-03 at 20:56 +0200, Ville Syrjälä wrote:
> On Thu, Jan 22, 2009 at 10:12:04PM +0200, Ville Syrjälä wrote:
> > On Thu, Jan 22, 2009 at 08:22:48PM +0200, Risto Suominen wrote:
> > > Since the complete re-write in 2.6.10, some PowerMacs (At least PowerMac 5500
> > > and PowerMac G3 Beige rev A) with ATI Mach64 chip have suffered from unstable
> > > columns in their framebuffer image. This seems to depend on a value (4) read
> > > from PLL_EXT_CNTL register, which leads to incorrect DSP config parameters to
> > > be written to the chip. This patch uses a value calculated by aty_init_pll_ct
> > > instead, as a starting point.
> > 
> > AFAICS it should be the right thing to do on other systems too. I have
> > a good collection of mach64 pci cards and laptops so I'll try to find
> > some time next week to test that theory on x86.
> 
> Well, the experiment failed on the first Mobility I tried. The FIFO
> calculations aren't obvious from the code and there's no mention how
> to actually calculate them in the programming guide. So I guess special
> casing powermacs is the best way forward.

There's one powermac with a M1 (the first clamshell ibook). I don't have
such a machine however, it would be useful if somebody who did could
test if the patch caused a regression there...

It's possible that we should instead base the code on the chip variant.

Ben.


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