[PATCH v8 2/2] arm-soc: Add support for arm-based tango4 platforms

[Måns Rullgård]

Marc Gonzalez <marc_gonzalez at sigmadesigns.com> writes:

> On 03/11/2015 17:37, Santosh Shilimkar wrote:
>> On 11/3/2015 2:12 AM, Måns Rullgård wrote:
>>> Marc Gonzalez writes:
>>>
>>>> Santosh Shilimkar wrote:
>>>>
>>>>> Mark Rutland wrote:
>>>>>
>>>>>> We didn't. Having a look just now, the earliest example appears to be
>>>>>> in OMAP4 L2 support patches back in 2009 [1]. I was not able to find a
>>>>>> rationale.
>>>>>>
>>>>>> Given that the MMU is on (and speculative accesses are permitted) I
>>>>>> can't see what the DSB achieves -- it can't quiesce the memory system.
>>>>>>
>>>>>> Santosh, any idea?
>>>>>
>>>>> IIRC, it was requirement from the OMAP ROM code to have a dsb before
>>>>> we call the SMC routine. I can't recollect more than that now.
>>>>
>>>> In that case, shouldn't dsb have been added to the ROM code,
>>>> on the "other side" of the smc, so as to not depend on Linux
>>>> code "getting it right"?
>>>
>>> You're new to this, aren't you? :)
>>
>> :-) Indeed. ROM code is burned into the chip and can't be changed.
>
> Oh, that kind of ROM... I thought EEPROM.
> (Our secure OS is stored in NAND flash.)
>
> If I'm bored, I'll try measuring the run-time difference with
> and without dsb.

Don't bother.  This is only used during initialisation anyway.  If that
takes a few microseconds longer, you won't be able to tell.

-- 
Måns Rullgård
mans at mansr.com