Date: Thu, 22 Jan 2009 22:12:04 +0200
From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= <syrjala@sci.fi>
To: Risto Suominen <risto.suominen@gmail.com>
Cc: Alex Kern <alex.kern@gmx.de>, linux-kernel@vger.kernel.org,
       benh@kernel.crashing.org, linux-fbdev-devel@lists.sourceforge.net
Subject: Re: [PATCH] atyfb: fix distorted image on PowerMacs
Message-ID: <20090122201204.GD4996@sci.fi>
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	Alex Kern <alex.kern@gmx.de>, linux-kernel@vger.kernel.org,
	benh@kernel.crashing.org, linux-fbdev-devel@lists.sourceforge.net
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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.

Also cc:ing fbdev-devel...

> Signed-off-by: Risto Suominen <Risto.Suominen@gmail.com>
> ---
> The testing is done on kernel version 2.6.18.
> 
> --- a/drivers/video/aty/mach64_ct.c.org	2006-09-20 06:42:06.000000000 +0300
> +++ b/drivers/video/aty/mach64_ct.c	2009-01-22 14:28:13.000000000 +0200
> @@ -7,6 +7,7 @@
>  #include <linux/delay.h>
>  #include <asm/io.h>
>  #include <video/mach64.h>
> +#include <asm/machdep.h>
>  #include "atyfb.h"
> 
>  #undef DEBUG
> @@ -536,6 +537,14 @@ static int __init aty_init_pll_ct(const
>  	pll->ct.xclk_post_div_real = postdividers[xpost_div];
>  	pll->ct.mclk_fb_div = q * pll->ct.xclk_post_div_real / 8;
> 
> +#ifdef CONFIG_PPC
> +	if (machine_is(powermac)) {
> +		/* Override PLL_EXT_CNTL & 0x07. */
> +		pll->ct.xclk_post_div = xpost_div;
> +		pll->ct.xclk_ref_div = 1;
> +	}
> +#endif
> +
>  #ifdef DEBUG
>  	pllmclk = (1000000 * pll->ct.mclk_fb_mult * pll->ct.mclk_fb_div) /
>  			(par->ref_clk_per * pll->ct.pll_ref_div);

-- 
Ville Syrj?l?
syrjala@sci.fi
http://www.sci.fi/~syrjala/
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