Tejun Heo wrote:
ATAPI devices come with plethora of bugs and many ATA controllers have
trouble dealing with odd byte DMA transfers. The problem is currently
somewhat masked by not allowing DMA transfers if the transfer size
isn't aligned to 16 bytes plus partial masking in problematic LLDs.
This masking is taken verbatim from IDE and is far from perfection.
There's no fundamental explanation why this should be sufficient and
there are ATAPI devices which don't work with the IDE driver.
In addition, this mixture of PIO and DMA commands reduces test
coverage which is already insufficient considering the crazy number of
ATAPI devices out in the wild.
Also, these misc ATAPI commands usually transfer small amount of data
and are used infrequently. There isn't much to be gained from using
DMA. Combined with the fact that another OS which is probably the
only one that most ATAPI device vendors test against uses PIO for
these commands, it's much wiser to use PIO for these commands and
concentrate debugging efforts on getting PIO right for misc commands
and DMA for bulk transfer commands.
Private command type / transfer length filtering in sata_promise,
pata_it821x and pata_pdc2027x are removed as core layer filtering is
more conservative.
Signed-off-by: Tejun Heo <[EMAIL PROTECTED]>
The other patches were OK, but I'm still not happy about "punishing the
good guys"
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