Re: [PATCH] libata: use FLUSH_EXT only when driver is larger than LBA28 limit

[Tejun Heo <htejun@gmail.com>]

Tejun Heo wrote:
> Many drives support LBA48 even when its capacity is smaller than
> 1<<28, as LBA48 is required for many functionalities.  FLUSH_EXT is
> mandatory for drives w/ LBA48 support.
> 
> Interestingly, at least one of such drives (ST960812A) has problems
> dealing with FLUSH_EXT.  It eventually completes the command but takes
> around 7 seconds to finish in many cases thus drastically slowing down
> IO transactions.  This seems to be a firmware bug which sneaked into
> production probably because no other ATA driver including linux IDE
> issues FLUSH_EXT to drives which report support for LBA48 & FLUSH_EXT
> but is smaller than 1<<28 blocks.
> 
> This patch adds ATA_DFLAG_FLUSH_EXT which is set iff the drive
> supports LBA48 & FLUSH_EXT and is larger than LBA28 limit.  Both cache
> flush paths are updated to issue FLUSH_EXT only when the flag is set.
> Note that the changed behavior is more inline with the rest of libata.
> libata prefers shorter commands whenever possible.

Jeff, I think this should go into #uptream-fixes, too.  We shouldn't 
have issued FLUSH_EXT to < 1<<28 devices in the first place.

Thanks.

-- 
tejun