On 01/04/2010 10:16 AM, Alan Cox wrote:
If the drive immediately starts the UDMA protocol after a write to the
command register (as it probably will for the DMA WRITE command), then
we'll be accessing the taskfile in the middle of the UDMA setup, which
can't be good. It's certainly a violation of the ATA specs.
I concur entirely - that wants pushing into the upstream kernel ASAP and
if its ok backporting. May also be worth seeing if that fixes the funny
in the ALi setup.
How do you think one tests for command completion? :) There does not
seem to be a general problem reading AltStatus(BSY) during a DMA
transfer. IDE driver and other well known codebases have been doing
that for decades.
I think the undefined behavior is only where the AltStatus read occurs
before the 400ns period specified by ATA... excising the AltStatus read
there (ata_sff_pause) should be fine for PIO, but problematic for MMIO
chipsets that need posted writes flushed prior to the 400ns delay.
Jeff
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