Re: AW: PowerPC PCI DMA issues (prefetch/coherency?)

On Friday 11 September 2009 04:44:34 Benjamin Herrenschmidt wrote:

On Thu, 2009-09-10 at 13:30 -0700, Pravin Bathija wrote:

quoted

There is also a patch that was submitted for 440EPX a couple of years
back. The 440EPX SOC causes hangs with Memory Read Multiple (MRM)
commands. Whether MRM is used or not depends on the value of
PCI_CACHE_LINE_SIZE register. I see that the changes are no longer
present in linux 2.6.30+ kernels. Although the patch certainly resolved
the hang issue with Silicon Image 680 PATA card as the 680 driver
attempts to use MRM commands - I don't know if it would resolve the data
corruption issue. It is certainly worth trying in my opinion. Below is a
link to the patch submission:

http://git.denx.de/?p=linux-2.6-denx.git;a=commit;h=cffefde924123e685327
48dd58fcb780eab5e219

The changes in the above repository is a quick hack that can't be merged
as-is (and afaik hasn't been submitted).

If indeed we need to clamp the PCI cache line size on those critters,
then we need something in ppc4xx_pci.c to detect the need, set
pci_cache_line_size to 0 and eventually fixup the existing values in
devices in case u-boot don't have them right.

Care to send a patch ? :-)

It's already there. See commit:

5ce4b59653b2c2053cd9a011918ac1e4747f24cc

powerpc/4xx: Workaround for PPC440EPx/GRx PCI_28 Errata


Cheers,
Stefan