[PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier call

Stephen Warren swarren at wwwdotorg.org
Fri Apr 8 22:26:22 PDT 2016

On 04/08/2016 12:20 PM, Eric Anholt wrote:
> Stephen Warren <swarren at wwwdotorg.org> writes:
>> On 04/04/2016 09:44 PM, Eric Anholt wrote:
>>> dsb() requires an argument on arm64, so we needed to add "sy".
>>> Instead, take this opportunity to switch to the same smp_wmb() call
>>> that gic uses for its IPIs.  This is a less strong barrier than we
>>> were doing before (dmb(ishst) compared to dsb(sy)), but it seems to be
>>> the correct one.
>> I assume all MMIO is part of the ish domain?
>> If so, the series,
>> Acked-by: Stephen Warren <swarren at wwwdotorg.org>
> I don't know if this barrier implies ordering all the way out to AXI on
> this HW, but I don't think that's a requirement of this function.

My understanding was that the barrier was explicitly to work around a 
bug in the bus fabric of the SoC, and hence the barrier very much does 
have to affect the transaction all the way out to AXI. Re-reading 
BCM2835-ARM-Peripherals.pdf section 1.3 "Peripheral access precautions 
for correct memory ordering" seems to confirm this.

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