linux-kernel - Re: kernel won't boot on a Cyrix MediaGXm (Geode )

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Date:	Wed, 20 Aug 2008 13:03:59 +0200
From:	Juergen Beisert <jbe@...gutronix.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Samuel Sieb <samuel@...b.net>, linux-kernel@...r.kernel.org,
	"Rafael C. de Almeida" <almeidaraf@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Magnus Damm <magnus@...inux.co.jp>,
	takada <takada@....nifty.com>
Subject: Re: kernel won't boot on a Cyrix MediaGXm (Geode )

On Mittwoch, 20. August 2008, Ingo Molnar wrote:
> * Juergen Beisert <jbe@...gutronix.de> wrote:
> > On Mittwoch, 20. August 2008, Ingo Molnar wrote:
> > > * Samuel Sieb <samuel@...b.net> wrote:
> > > > Ingo Molnar wrote:
> > > >> any patch we should pick up to make your box boot?
> > > >
> > > > I've looked through various datasheets and found that the GXm and
> > > > GXLV Geode processors don't have an incrementor.  I attached two
> > > > patches. One only calls the incrementor setup for GX1 or better.  The
> > > > other one removes the incrementor setup entirely.  As the incrementor
> > > > value differs according to clock speed and we would hope that the
> > > > BIOS configures it correctly, it is probably the better one to
> > > > choose.  But I will leave that choice up to you.  Either one works
> > > > for me. :-)
> > >
> > > i went for the commit below and queued it up in tip/x86/urgent - thanks
> > > Samuel.
> > >
> > > what happens if the incrementor is not set up correctly by the BIOS
> >
> > The system can freeze. The clock the incrementor modifies is used for
> > the external SDRAM (something like a delay line or jitter reduction).
> > Thats why its setting depends on the core clock speed.
>
> so, what's the recommendation - is the patch fine? (which removes
> incrementor setting, leaving it to the BIOS)

In my environment I need the incrementor setting in accordance to the CPU core 
frequency, as my BIOS sets a wrong value. Removing it is no solution for me.

But: There where a few bug reports in the last weeks, and all had problems 
when the incrementor setting is changed inside the kernel. Seems only my BIOS 
is broken.

So I vote for removing the incrementor setting. I can life with a local patch 
for my kernels.

Juergen

-- 
Dipl.-Ing. Juergen Beisert | http://www.pengutronix.de
 Pengutronix - Linux Solutions for Science and Industry
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