Re: [PATCH 2.6.13 14/14] sas-class: SCSI Host glue

[James Bottomley <James.Bottomley@SteelEye.com>]

On Sun, 2005-09-11 at 05:56 +0200, ak@muc.de wrote:
> >> Naturally, aic94xx has _no limitations_. :-)  But hey, our hardware just 
> >> kicks a*s!
> >
> > That's very nice for you - but lets face it, a SAS layer
> > that'll be unable to also deal with the El-Cheapo brand
> > controllers isn't going to be very useful.
> 
> Nobody knows what these bu^wlimitations will be though. So you cannot
> really plan for them in advance.  When someone writes drivers for such 
> limited hardware they can add code to handle the limitations. But it 
> seems reasonable to start with a clean hardware model, and only
> add the hacks later when they are really needed and the requirements
> are understood.

But my point was that we already have a mechanism for coping with this:
The scsi template parameterises some of these things (max sector size,
sg table elements, clustering, etc).  For less standard things it
doesn't cover the driver uses the blk_ adjustors directly from
slave_alloc/slave_configure (This is currently how USB and firewire
communicate their alignment requirements).

By wrappering both the template and the slave_alloc/slave_configure
methods in the SAS class and not providing the driver access, it can't
use existing methods to make any adjustments that may be necessary.

James