Re: [PATCH] fsldma: use PCI Read Multiple command

David Hawkins
2009-04-27T20:23:00Z

Hi Timur,

>> Would you like some sort of summary of this info for a commit
>> message?
>
> That's probably overkill. I just want a sentence or two that tells
> someone looking at the code casually that the behavior of reading PCI
> memory might be different than what they expect.

Could you help us with the wording you'd like to see in the code.
Did you want to see something in the header comments, or something
near the register settings?

How about something like this in place of the existing PCI_RM
comment:

PRC_RM - PCI read multiple
The default PCI read command used by the DMA controller is
PCI Read (PCI command 6h). When the burst length is 32-bytes
or longer, PCI Read Line (PCI command Eh) is used (undocumented
feature of the controller). Using PCI read multiple
(PCI command Ch) results in high-performance across PCI
bridges. DMA transfers to non-prefetchable PCI registers
should not result in prefetched reads, even when using
the PCI read multiple command.

Cheers,
Dave