On Wed, Aug 28, 2013 at 08:46:38PM +0100, Grant Likely wrote: > On Thu, 22 Aug 2013 14:59:30 +0100, Mark Rutland <mark.rutland@xxxxxxx> wrote: > > On Mon, Aug 19, 2013 at 02:56:10PM +0100, Sudeep KarkadaNagesha wrote: > > > On 19/08/13 14:02, Rob Herring wrote: > > > > On 08/19/2013 05:19 AM, Mark Rutland wrote: > > > >> On Sat, Aug 17, 2013 at 11:09:36PM +0100, Benjamin Herrenschmidt wrote: > > > >>> On Sat, 2013-08-17 at 12:50 +0200, Tomasz Figa wrote: > > > >>>> I wonder how would this handle uniprocessor ARM (pre-v7) cores, for > > > >>>> which > > > >>>> the updated bindings[1] define #address-cells = <0> and so no reg > > > >>>> property. > > > >>>> > > > >>>> [1] - http://thread.gmane.org/gmane.linux.ports.arm.kernel/260795 > > > >>> > > > >>> Why did you do that in the binding ? That sounds like looking to create > > > >>> problems ... > > > >>> > > > >>> Traditionally, UP setups just used "0" as the "reg" property on other > > > >>> architectures, why do differently ? > > > >> > > > >> The decision was taken because we defined our reg property to refer to > > > >> the MPIDR register's Aff{2,1,0} bitfields, and on UP cores before v7 > > > >> there's no MPIDR register at all. Given there can only be a single CPU > > > >> in that case, describing a register that wasn't present didn't seem > > > >> necessary or helpful. > > > > > > > > What exactly reg represents is up to the binding definition, but it > > > > still should be present IMO. I don't see any issue with it being > > > > different for pre-v7. > > > > > > > Yes it's better to have 'reg' with value 0 than not having it. > > > Otherwise this generic of_get_cpu_node implementation would need some > > > _hack_ to handle that case. > > > > I'm not sure that having some code to handle a difference in standard > > between two architectures is a hack. If anything, I'd argue encoding a > > reg of 0 that corresponds to a nonexistent MPIDR value (given that's > > what the reg property is defined to map to on ARM) is more of a hack ;) > > > > I'm not averse to having a reg value of 0 for this case, but given that > > there are existing devicetrees without it, requiring a reg property will > > break compatibility with them. > > Then special cases those device trees, but you changing existing > convention really needs to be avoided. The referenced documentation > change is brand new, so we're not stuck with it. I have no problem with changing the bindings and forcing: #address-cells = <1>; reg = <0>; for UP predating v7, my big worry is related to in-kernel dts that we already patched to follow the #address-cells = <0> rule (and we had to do it since we got asked that question multiple times on the public lists). What do you mean by "special case those device trees" ? I have not planned to patch them again, unless we really consider that a necessary evil. Thanks, Lorenzo -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
