Re: TASKFILE ioctl for libata?

[Timothy Thelin <timothy.thelin@wdc.com>]

On Fri, 2006-02-17 at 03:38 -0500, Jeff Garzik wrote:
> Tejun Heo wrote:
> > Just a side note.  Taskfile has finer granuality regarding which 
> > registers are written and read back than current libata does and IDE 
> > taskfile implementation is somewhat broken/weird in a few delicate fun 
> > ways, so... be careful.  Whoever tries it.
> 
> Yes -- it opens the question about whether we care enough to fully 
> support flagged taskfiles, and if not, how to best emulate that support 
> under libata.
> 
> I'm told that flagging individual ATA shadow registers for modification 
> (or not) is required for issuing certain specialized PATA 
> vendor-specific commands.  SATA, OTOH, transmits all ATA shadow 
> registers in a FIS, so flagged taskfiles are useless.
> 
> So, I'm now thinking the best route is to leave the code as it is ;-) 
> Rather than imperfectly implementing the flagged taskfile ioctl, punt 
> the remaining userland users to SG_IO.
> 
> I don't see lack of full flagged taskfile support as a big stumbling 
> block to libata use.
> 
> 	Jeff

FYI, Western Digital doesn't need flagged taskfile access to use its
vendor specific commands; SAT passthru works fine (although we'd
appreciate more of the protocols implemented, or at least a way to
discover at runtime which ones are implemented before trying to use
them).

- Tim Thelin