[U-Boot] Uboot and ARM SMP support

[Nishanth Menon]

Shilimkar, Santosh said the following on 06/25/2009 04:51 PM:
>> -----Original Message-----
>> From: Pandita, Vikram 
>> Sent: Thursday, June 25, 2009 6:32 PM
>> To: Jean-Christophe PLAGNIOL-VILLARD; Nishanth Menon; 
>> Shilimkar, Santosh
>> Cc: Sudeep K N; u-boot at lists.denx.de; Tom
>> Subject: RE: [U-Boot] Uboot and ARM SMP support
>>
>> Adding Santosh to loop who has pushed the OMAP4 SMP support 
>> into Kernel.org
>>
>>
>>     
>>> -----Original Message-----
>>> From: Jean-Christophe PLAGNIOL-VILLARD [mailto:plagnioj at jcrosoft.com]
>>> Sent: Thursday, June 25, 2009 7:44 AM
>>> To: Nishanth Menon
>>> Cc: Sudeep K N; u-boot at lists.denx.de; Pandita, Vikram; Tom
>>> Subject: Re: [U-Boot] Uboot and ARM SMP support
>>>
>>> On 12:47 Thu 25 Jun     , Nishanth Menon wrote:
>>>       
>>>> Sudeep K N said the following on 06/25/2009 12:11 PM:
>>>>         
>>>>> Sorry, may be I confused you.
>>>>> I indent to use only one core for u-boot.
>>>>> I wanted to ask whether we need to update the cache
>>>>> management to boot for ARM Cortex A9 SMP if we take
>>>>> ARM Cortex A8 code as base.
>>>>> I have tried and did not require any change on top of A8 code
>>>>> to run u-boot on A9 SMP.
>>>>> Is that right approach?
>>>>>
>>>>>
>>>>>           
>>>> you may want to see [1] how this was done for OMAP4 (which 
>>>>         
>> has a SMP
>>     
>>>> cortex A9)-> we can discuss how to setup cortex_a9 in 
>>>>         
>> mainline u-boot.
>>     
>>>> My thought would be: cpu/arm_cortexa9 - considering that 
>>>>         
>> a9 cores could
>>     
>>>> be from 1 to 4 or so if my memory serves right -> btw, I 
>>>>         
>> wonder how SMP
>>     
>>>> handling is done in u-boot today..
>>>>         
>>> for arm I've only a theorical design as I've no SMP board for now
>>> but I want to see SMP boot & AMP boot supported in Mainline
>>>
>>>       
>
> The approach is perfect and that's what is most of the SMP systems are doing..
> If one look at the linux framework, U-boot need not know about the secondary cores.
>
> As far as caches goes, the SCU is not enabled at u-boot level so there is no coherency
> between L1 caches.L2 is external and not enabled at u-boot level for time being.
> At the point when u-boot transfer control to kernel, the caches are flushed in the 
> clean-up path so you need not do any explicit stuff.
>
> In case you want to enable L2 cache ( if preset ), then you need to add support for 
> that in the u-boot. 
>
> So essentially u-boot would be almost same as Cortex-A8 except you should avoid programming AuxControl
> register because the bit definitions are different.
>
> Hope this helps
>   
so how would the new arch look like? do we do:
cpu/arm_cortexa8_9 and common code there?
Regards,
Nishanth Menon