Re: Proposals to change the way all drivers work with SCSI commands

[Jeff Garzik <jeff@garzik.org>]

James Bottomley wrote:
> On Fri, 2007-05-11 at 15:15 -0400, Jeff Garzik wrote:
>> James Bottomley wrote:
>>> Right at the moment, we're planning to clean up the way SCSI drivers
>>> process commands.  The proposals are essentially:
>>>
>>>      1. Get rid of the now unnecessary map_single path (every command is
>>>         either zero transfer or scatter/gather)
>>>      2. use accessors to manipulate the SG lists (mainly so that we can
>>>         alter the implementation without affecting the drivers)
>>>
>>> It strikes me that in all of this, we could also consider doing the DMA
>>> mapping inside the mid layer (instead of in every driver).  This is
>>> essentially what libata is already doing ... leading to confusion in
>>> SCSI drivers that use libata for SATA.
>> My eyes are crossed :)  How does doing DMA mapping in the mid layer lead 
>> to confusion in SCSI drivers that use libata for SATA?  Are you talking 
>> about aic94xx and ipr only, or other drivers?
> 
> Those are the only two that use libata for SATA, yes.
> 
> aic94xx is horrible in this regard ... it has to try to distinguish STP
> commands that come from libsas (and thus aren't mapped) from ones that
> come from libata which are ... and it still doesn't get it entirely
> right.

I would lean towards fixing libata to -not- DMA-map for those drivers. 
Splitting up DMA mapping is ugly.

	Jeff