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

Kumar Gala galak at kernel.crashing.org
Thu Sep 13 01:14:29 EST 2007

On Sep 12, 2007, at 9:45 AM, Josh Boyer wrote:

> 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.

I assume you'll be adding to the 'quirk' flags that we already have  
in place.

- k

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