Re: [PATCH 3/5] ARM: vexpress: Add DT support in v2m

[Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>]

On Thu, Nov 17, 2011 at 06:37:26PM +0000, Dave Martin wrote:
> On Thu, Nov 17, 2011 at 04:05:37PM +0000, Russell King - ARM Linux wrote:
> > You do understand that system_rev is for the system _revision_ not for
> > some kind of system ID.  For example, it's to identify whether we're on
> > a revision 4, 5 or 6 system.
> > 
> > However, with DT the differences in system revision should be encoded
> > into the DT itself, and the kernel should not be making choices about
> > the hardware off this.
> 
> I can't comment on whether this is an abuse of system_rev, since I'm
> not too familiar with that.
> 
> I feel that Whether the value of the V2M_SYS_ID register should be put
> in the DT is more doubtful though: the DT must describe the hardware
> which cannot be probed.

That is exactly my point - but we don't want V2M_SYS_ID controlling what
hardware is there because then you'll end up having _drivers_ having to
be aware of the system revision.

Instead, the differences in device IP - when they're not discoverable
from the device itself - should be encoded in DT to allow the device IP
to be reused on different platforms which may not even have a V2M_SYS_ID
register.

That's what my objection is about: nothing should be using the overall
system revision to determine anything about it.