Re: [PATCH 05/07] sata_mv: mv_fill_sg fixes

[Mark Lord <liml@rtr.ca>]

Grant Grundler wrote:
> On Fri, Jan 30, 2009 at 3:50 PM, Mark Lord <liml@rtr.ca> wrote:
..
>>
>>        if (likely(last_sg))
>>                last_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
>> +       mb(); /* ensure data structure is visible to the chipset */
> 
> It's not obvious to me what you are racing against here.
> Normally the mb() is to prevent the above store from getting executed
> *after* some MMIO read or write that would tell the chip to read the
> flags_size field (or anything recently stored in that data structure).
> 
> I guess I'm asking for the comment to indicate which MMIO write it's
> racing with.
..

It's exactly the same as the generic routine in libata-sff,
which has a mb() in the same place for the same reason:
To ensure the PRD table is visible to the chipset
before we trigger the I/O operation.

Pretty standard.