linux-kernel - Re: Hang in fb_notifier_call_chain with nvidia framebuffer

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Date:	Sun, 08 Oct 2006 01:14:47 -0700
From:	Wink Saville <wink@...ille.com>
To:	Andrew Morton <akpm@...l.org>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Matthias Hentges <oe@...tges.net>,
	linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net
Subject: Re: Hang in fb_notifier_call_chain with nvidia framebuffer

Andrew Morton wrote:
> On Wed, 04 Oct 2006 09:26:04 -0700
> Wink Saville <wink@...ille.com> wrote:
> 
>> Attached in the zip file is:
>>
>> log-hang1.txt	-> log showing hang
>> cfg-hang1	-> config file for hang condition
>> cfg-ok		-> config file that works
>> fbmem.c		-> Modifications to register_framebuffer
>>
>> To possibly assist I turned on debugging in nvidia.c and found that it 
>> hung in the call to register_framebuffer. I then added some additional 
>> debug in that routine and it appears the hang occurs in the call to 
>> fb_notifier_call_chain.
>>
>> Please let me know what else maybe needed.
> 
> Please:
> 
> - get sysrq working:
> 
> 	set CONFIG_MAGIC_SYSRQ=y, rebuild, reboot
> 	echo 1 > /proc/sys/kernel/sysrq
> 	dmesg -n 8
> 
> - make it hang
> 
> - Hit alt-sysrq-T
> 
> - Send us the resulting output
> 
> Thanks.
> -
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> 

Andrew,

Thank you for the reply, I believe I've found the reason frame buffer doesn't
work on my system, there is a divide by zero occurring at line 157 of
nvGetClocks in ./drivers/video/nvidia/nv_hw.c.

(Note: The screwy output below is due to hacking drivers/serial/8250.c to add two
routines serial_putchar and serial_putchars so that I could make progress looking
for the bug, as printk stopped working at acquire_console_sem called from bind_con_driver.)

Last portion of the output:

@[   97.643286] take_over_console: call bind_con_driver csw=ffffffff805d8600 first=0, last=62, deflt=1
@[   97.652521] bind_con_driver: E
@[   97.655774] bind_con_driver: acquire_console_sem
@1[   97.660604] acquire_console_sem: drivers/char/vt.c:bind_con_driver:2752
@!2345689abABCDEF<fb_con_init>abcdefghij<nvidiafb_set_par>abcd<nvidia_calc_regs>bdjkl<NVCalcStateExt>acei<nv30UpdateArbitrationSettings>a<nv
GetClocks>N=83 NB=0 freq=27000 M=3 MB=0 P=0

>From the above output we see MB=0 and hence death at line 157:

*MClk = ((N * NB * par->CrystalFreqKHz) / (M * MB)) >> P;

It would seem that my hardware (7600 GT K0) is not supported by the driver?
It should also be noted that there are quite a number of divisions
in the nv_hw.c that have no protection against divide by zeros.


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