MTD and XIP

[Nicolas Pitre]

On Sat, 6 Nov 2004, Nicolas Pitre wrote:

> On Fri, 5 Nov 2004, Dan Post wrote:
> 
> > Do you have a specific reason to always disable write suspend on XIP
> > kernels?  That's a pretty big latency hit, and I don't think we need
> > to disable it for XIP systems.
> > I saw your comment that "the XIP system config appears to have
> > problems using write suspend at the moment".  Any specifics?
> 
> It was causing me jffs2 corruption problems and I couldn't figure out 
> why.  So after two days of bug chasing I gave up and disabled write 
> suspend, blaming the hardware.  I measured the IRQ latency hit to be in 
> the 400 usec range in that case.
> 
> If you want to have a look please be my guest. To reproduce the problem, 
> simply comment out the clearing of the write suspend bit and do:
> 
> 	eraseall /dev/mtd2
> 	mount -t jffs2 /dev/mtdblock2 /mnt
> 	cd /mnt
> 	tar -cvf test.tar /sbin
> 	tar -xvf test.tar
> 
> This was enough for jffs2 to complain about node totlen mismatch errors 
> and occasional CRC errors.

Oh and BTW you don't need to have your kernel actually XIP to test this.
A standard kernel but with CONFIG_MTD_XIP enabled will show the problem 
as well, and it makes the loading of new test kernels quicker (unless 
you do everything modular).


Nicolas