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

Marc Gonzalez [off-list ref] writes:

On 03/11/2015 17:37, Santosh Shilimkar wrote:

quoted

On 11/3/2015 2:12 AM, M?ns Rullg?rd wrote:

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Marc Gonzalez writes:

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Santosh Shilimkar wrote:

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Mark Rutland wrote:

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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.

-- 
M?ns Rullg?rd
mans at mansr.com