[POWERPC] PCI Bug fix for MRM failure in PPC 440EPx

Josh Boyer jwboyer at linux.vnet.ibm.com
Thu Sep 13 00:45:36 EST 2007

On Thu, 30 Aug 2007 10:33:28 +0200
Stefan Roese <ml at stefan-roese.de> wrote:

> Problem Description and Fix : Memory Read Multiples(MRM) do not work
> correctly on PPC 440EPX based systems. A PCI driver determines whether
> MRMs are supported by reading the PCI cache line size register. If this
> value is zero then MRMs are not supported. However some PCI drivers
> write to the PCI cache line size register on initialization. This
> results in MRMs being sent to system memory on 440EPX based systems.
> Since MRMs do not work correctly in 440EPX based systems this may cause
> system hang. This patch solves this problem by modifying the PPC
> platform specific PCI configuration register write function, by forcing
> any value written to PCI_CACHE_LINE_SIZE register to be 0. This fix was
> tested on different PCI cards : i.e. Silicon Image ATA card and Intel
> E1000 GIGE card. On Silicon Image ATA card without this fix in place
> creating a filesystem on IDE drive "mke2fs /dev/hda" was hanging the
> system. MRMs issued by the PCI card were seen on the PCI analyzer since
> the Silicon Image driver was setting the PCI_CACHE_LINE_SIZE register to
> 255. With this patch the PCI_CACHE_LINE_SIZE register was 0 and only
> Memory Reads were seen on PCI analyzer.
> Signed-off-by: Pravin M. Bathija <pbathija at amcc.com>
> Signed-off-by: Stefan Roese <sr at denx.de>
> ---
> I know this patch is a little "dirty", but perhaps somebody has a better
> idea to fix this problem. Thanks.

For the peanut gallery, Stefan and I discussed this a bit on IRC today
and a different approach for arch/powerpc is going to be looked at
instead.  Namely, introducing a new flag for indirect_type in the
pci_controller structure to key off of instead of having ifdefs.


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