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SubjectRe: [PATCH] libata_acpi: A different strategy for using ACPI information
Alan Cox wrote:
> Lots of BIOSen simply return the BIOS set modes via the ACPI methods and
> pass back the values you give it across suspend/resume. Thus instead of
> trying to do clever stuff with this data we instead use it as a way to
> take a sneak peak at cable type information when viable. This should help
> us catch more of the laptops that do weird stuff, the VIA SATA bridges
> and the totally horked Nvidia cable handling.
> For now its only used by the VIA and AMD/NV driver until we get a better
> idea of whether this is a sensible idea or not.
> Opinions ?
> Signed-off-by: Alan Cox <>

Looks fairly reasonable to me. However, I suspect any use of _GTM is
somewhat dangerous (at least after the resume) unless we use the _STM
and _GTF methods in the proper sequence when resuming. (Is that in the
-mm tree now?)

Keep in mind that in the pata_acpi case where we don't do anything to
program the hardware directly, we can still use _STM to program a lower
speed than the BIOS chose if we decide to do this. Windows does indeed
do this (you can force PIO mode in the control panel, and it will also
reduce UDMA speeds or drop to PIO if there are too many CRC errors or
timeouts), so this should be safe. We just had better be sure that the
speed we give it is valid, since there is no sane way for the function
to indicate failure. (Thus the problem with the "cram in all possible
values to see what it supports" strategy for determining mode limits..)

Robert Hancock Saskatoon, SK, Canada
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