Re: Hang in fb_notifier_call_chain with nvidia framebuffer

[Wink Saville <wink@saville.com>]

Andrew Morton wrote:
> On Wed, 04 Oct 2006 09:26:04 -0700
> Wink Saville <wink@saville.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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