_GTM fetches currently configured transfer mode while _STM configures
controller according to _GTM parameter and prepares transfer mode
configuration TFs for _GTF. In many cases _GTM and _STM
implementations are quite brittle and can't cope with configuration
changed by libata.
libata does not depend on ATA ACPI to configure devices. The only
reason libata performs _GTM and _STM are to make _GTF evaluation
succeed and libata also doesn't care about how _GTF TFs configure
transfer mode. It overrides that configuration anyway, so from
libata's POV, it doesn't matter what value is feeded to _STM as long
as evaluation succeeds for _STM and following _GTF.
This patch adds dev->__acpi_init_gtm and store initial _GTM values on
host initialization before modified by reset and mode configuration.
If the field is valid, ata_acpi_init_gtm() returns pointer to the
saved _GTM structure; otherwise, NULL.
This saved value is used for _STM during resume and peek at
BIOS/firmware programmed initial timing for later use. The accessor
is there to make building w/o ACPI easy as dev->__acpi_init doesn't
exist if ACPI is not enabled.
On driver detach, the initial BIOS configuration is restored by
executing _STM with the initial _GTM values such that the next driver
can also use the initial BIOS configured values.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
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