Re: [PATCH 02/02] sata_mv: warn on PIO with multiple DRQs

[Mark Lord <liml@rtr.ca>]

Jeff Garzik wrote:
> Mark Lord wrote:
>> Chip errata sometimes prevents reliable use of PIO commands which involve
>> more than a single DRQ (data request).  In normal operation, libata 
>> should
>> not generate such PIO commands (uses DMA instead), but they could be sent
>> in via SG_IO from userspace.
>>
>> A full workaround might be to break up such commands into sequences
>> of single DRQ ones, but that's just way too complex for something
>> that doesn't normally happen in real life.
>>
>> So, allow the attempt (it often works, despite the errata),
>> but log the event for reference when somebody screams.
>>
>> Signed-off-by: Mark Lord <mlord@pobox.com>
> 
> 
> applied patches 1-2
> 
> 
> 
>> Tejun/Alan/Jeff:
>>
>> We may also want a patch to prevent libata-eh from downshifting
>> all the way to PIO on these chipsets, but I am not sure how to
>> accomplish that from inside sata_mv.  Any suggestions?
> 
> Do we really want that?  Seems to me we need that for older bridged PATA 
> devices attached to a SATA bridge.
..

Just about everything can do some form of DMA nowadays,
but regardless of that the sata_mv chipsets have errata
for PIO of anything more than a single sector.

In practice, I haven't managed to trigger the issue here,
but the errata descriptions indicate that it should be a major
issue for any volume of multi-sector PIO commands.

Cheers