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

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Message-ID: <20090203185624.GC22401@sci.fi>
Date:	Tue, 3 Feb 2009 20:56:25 +0200
From:	Ville Syrjälä <syrjala@....fi>
To:	Risto Suominen <risto.suominen@...il.com>,
	Alex Kern <alex.kern@....de>, linux-kernel@...r.kernel.org,
	benh@...nel.crashing.org, linux-fbdev-devel@...ts.sourceforge.net
Subject: Re: [Linux-fbdev-devel] [PATCH] atyfb: fix distorted image on
	PowerMacs

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.

-- 
Ville Syrjälä
syrjala@....fi
http://www.sci.fi/~syrjala/
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