Subject: Re: [PATCH] powerpc/4xx: Workaround for PPC440EPx/GRx PCI_28 Errata

From: Stefan Roese <[email-masked]>
Date: Thu, 12 Jun 2008 16:24:13 +0200

On Wednesday 11 June 2008, Josh Boyer wrote:
> The 440EPx/GRx chips don't support PCI MRM commands.  Drivers determine
> this by looking for a zero value in the PCI cache line size register. 
> However, some drivers write to this register upon initialization.  This can
> cause MRMs to be used on these chips, which may cause deadlocks on PLB4.
>
> The workaround implemented here introduces a new indirect_type flag, called
> PPC_INDIRECT_TYPE_BROKEN_MRM.  This is set in the pci_controller structure
> in the pci fixup function for 4xx PCI bridges by determining if the bridge
> is compatible with 440EPx/GRx.  The flag is checked in the
> indirect_write_config function, and forces any writes to the
> PCI_CACHE_LINE_SIZE register to be zero, which will disable MRMs for these
> chips.
>
> A similar workaround has been tested by AMCC on various PCI cards, such as
> the Silicon Image ATA card and Intel E1000 GIGE card.  Hangs were seen with
> the Silicon Image card, and MRMs were seen on the bus with a PCI analyzer.
> With the workaround in place, the card functioned properly and only Memory
> Reads were seen on the bus with the analyzer.
>
> Signed-off-by: Josh Boyer <[email-masked]>

Acked-by: Stefan Roese <[email-masked]>

I manually applied your patch (since it doesn't apply clean as discussed on 
IRC) and tested it on my Sequoia with a modified PCI USB driver changing 
PCI_CACHE_LINE_SIZE.

Best regards,
Stefan