Re: [PATCH] ARM: Update SMP_ON_UP code to detect A9MPCore with 1 CPU devices

[Santosh Shilimkar <santosh.shilimkar@ti.com>]

On Friday 23 August 2013 01:08 PM, Sekhar Nori wrote:
> On 8/13/2013 7:01 PM, Santosh Shilimkar wrote:
>> On Tuesday 13 August 2013 07:19 AM, Will Deacon wrote:
>>> On Mon, Aug 12, 2013 at 07:34:13PM +0100, Santosh Shilimkar wrote:
>>>> On Friday 02 August 2013 11:48 AM, Will Deacon wrote:
>>>>> I think this an A9-specific register, which reads as 0 on UP A9 and reads as
>>>>> some form of PERIPH_BASE for SMP parts. The issue I have is when PERIPH_BASE
>>>>> is zero.
>>>>>
>>>> What do we do here ? Should we document this in the code and proceed ?
>>>> Mostly there is no platform with PERIPH_BASE = 0, so its should be fine but
>>>> I am open for any other alternative.
>>>
>>> The only other alternative I can think of is forcing people to have
>>> CONFIG_SMP=n, but that blows away single zImage for your platform.
>>>
>> Yep which surely we don't want considering after so much effort we
>> have it working first place. How about going ahead with assumption
>> that PERIPH_BASE = 0 case doesn't work.
> 
> I must be missing something but why cannot we use the SCU configuration
> register "CPU number" field to determine that its a UP? I do not have an
> OMAP4 board, but on AM437x, it certainly indicates only CPU0 present.
> 
Thats what patch does. Yes, you are missing the point of dicussion. 
On real UP Cortex-A9, the base address read will return '0' which is
treated as invalid address in the patch. Will D pointed out that one
can build a SOC where PERIPH_BASE can be 0 so thats not safe.
Thats the only contention left here.

Will, Russell,
Am just re-asking the question about whether we can ignore PERIPH_BASE = 0
and just document in the code about the limitation.

regards,
Santosh