linux-kernel - Re: sc3200 cpu + apm module kernel crash

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Date:	Sun, 5 Nov 2006 22:33:58 +0100
From:	"Nicolas FR" <nicolasfr@...il.com>
To:	"Alan Cox" <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: sc3200 cpu + apm module kernel crash

I have finally traced down the bug (Tatung webpad TWN-5213CU with SC3200 CPU):

- in apm_mainloop there is an for(;;) loop, which set a
scheduler_timeout (1second) and then calls apm_event_handler().

- apm_event_handler does some checks and calls check_events();

- check_events has a loop:
	while ((event = get_event()) != 0) { switch (event) {...} }

The module was "crashing" on my box because it keeps on receiving
events=APM_UPDATE_TIME meaning that it would never get out of the
while() loop in check_events. I need to do some tests but I might
simply fix this by ignoring APM_UPDATE_TIME events. I first thought
replacing the "while ((event = get_event()) != 0)" by an "if ((event =
get_event()) != 0)" but maybe I would miss other events doing this?


Best regards,
Nicolas.

PS: btw, thanks for your email that's really nice to answer every
message on this mailing list.

On 11/5/06, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> Ar Sad, 2006-11-04 am 00:06 +0100, ysgrifennodd Nicolas FR:
> > I have thrown a bunch of  "printk(KERN_INFO "apm: I am here\n");" and
> > noticed the crash is happening just when calling apm_event_handler();
> > and does not even execute any instruction in this function... This is
> > the point I don't understand, how can it crash just on calling a
> > function and not executing the first statement in this function?
>
> APM is BIOS code so the assembler inlines trap into the firmware and the
> firmware sometimes isn't very good, particularly the 32bit entry points
> which are not used by a certain other vendors products.
>
> In those cases you need to trace the asm code in the firmware and see if
> the firmware is buggy.
>
>
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