Re: [PATCH 14/14] libata: use PIO for misc ATAPI commands

[Jeff Garzik <jeff@garzik.org>]

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 <htejun@gmail.com>

The other patches were OK, but I'm still not happy about "punishing the 
good guys"