lkml.org 
[lkml]   [2013]   [Aug]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC PATCH v2 3/4] powerpc: refactor of_get_cpu_node to support other architectures
    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.

    Mark.


    \
     
     \ /
      Last update: 2013-08-22 16:21    [W:4.379 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site