Re: 2.6.32: Promise UDMA33 card refuses to work in UDMA mode

[Jeff Garzik <jeff@garzik.org>]

On 01/04/2010 09:06 PM, Robert Hancock wrote:
> Indeed, which is why I suspect that a global change to handle this
> controller may not be a good idea. Overriding sff_exec_command for this
> driver to not do the altstatus read (just wait 600ns, maybe) might be
> the best solution for now.


Well, I think it's fair to say that this should be applied more 
generally than just one driver.  It is definitely conceivable that 
reading AltStatus causes a problem with more than one host controller, 
even though the ATA7 and ATA8 state diagrams recommends doing so.

One solution could be taken from the old-IDE driver: handle things at 
the other end of the transaction.  Audit the paths that check status at 
the end of a drive command, rather than focusing on the start of the 
transaction.

That is where the "hard requirements" exist, anyway.  ATA requires us to

* wait 400ns before reading Status, and/or
* wait one PIO cycle before reading Status

And logically, we only need to read Status at the end of the 
transaction, or when handling a non-DMA PCI shared interrupt.

	Jeff