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

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:

quoted

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.