Re: [PATCH] [1/22] Add new sense_buffer_mask host template field

[Andi Kleen <andi@firstfloor.org>]

On Mon, Feb 25, 2008 at 06:48:28AM -0800, James Bottomley wrote:
> On Mon, 2008-02-25 at 00:35 +0100, Andi Kleen wrote:
> > sense buffers are something that still needs to be explicitely 
> > bounced in the scsi layer. Instead of using the global unchecked_isa_dma
> > flag define a special fine grained mask for this.
> > 
> > I decided to use a full dma mask because that is most useful for some future
> > infrastructure work I'm doing.
> 
> Why do we need a separate mask?  Why can't we just use the device
> dma_mask?

First a lot of drivers don't need it because they handle the sense
buffers without DMA. So if we just used a device mask we would either
do unnecessary work for those or require a special sense buffer
mask in the device (which wouldn't belong into the device layer) 

Then there isn't really a device anywhere in these drivers and I didn't
plan to rewrite them to add one. 

So just having a SCSI specific sense buffer mask seemed best. It is
only set when a ISA driver actually does sense buffer DMA, which
is only true in a handful of drivers.

-Andi