linux-kernel - Re: bcm33xx port

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Message-Id: <200806081527.31221.luke@dashjr.org>
Date:	Sun, 8 Jun 2008 15:27:28 -0500
From:	Luke -Jr <luke@...hjr.org>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mips@...ux-mips.org
Subject: Re: bcm33xx port

On Sunday 08 June 2008, Maciej W. Rozycki wrote:
> On Sun, 8 Jun 2008, Luke -Jr wrote:
> > the bcm63xx patches OpenWrt has that I'm using as a base for this...
>
>  It would be best if the patches you are referring to got merged with the
> mainline.  Otherwise whoever uses them is essentially on their own --
> people lack the resources needed to chase random changes out there in
> general.

Is merging with mainline something I can help with, being a beginner in this 
area generally and not having any part in writing them?

> > >  That's grossly wrong.  If you need to preset it for the time being
> > > till you debug calibration, then for a MIPS processor assume one
> > > instruction per clock tick and two instructions per loop -- that may
> > > not be entirely correct, but is a good approximation.  Otherwise you
> > > risk peripheral devices are not driven correctly with all sorts of the
> > > nasty results.
> >
> > Meaning this?
> > 	preset_lpj = loops_per_jiffy = 2;
>
>  Not exactly.  Try harder -- this is simple arithmetic and you've got all
> the data given above already. :)

200 / 2? I'm not really sure what a 'jiffy' is..

> > > and (b) control being transferred to a block of memory that isn't
> > > actually code, as can happen if exception vectors or global
> > > pointers-to-functions aren't set up correctly, or if the kernel stack
> > > is being corrupted.   When you say "the instruction in question is a
> > > store word", how do you know that?
> >
> > The RI error spits out a bunch of info, including epc which presumably
> > points to the instruction causing the problem: ac85ffc0; this is 'sw
> > a1,-64(a0)'
>
>  I have seen that already and wrote these stores in __bzero are protected.
> Perhaps the fixup fails for some reason, but you need to investigate it
> and this is why I suggested to see how the RI handler is reached.  Since
> this is a known point the failure leads to, you should be able to work
> backwards from there quite easily.

Ah, so what you're saying is that perhaps the 'sw' is triggering a TLB 
exception, and the handler for *that* is causing the RI problem?

Thanks,

Luke
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