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

From	Stephen Warren <swarren@wwwdotorg.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier call
Date	2016-04-09 07:30 +0200
Message-ID	<rlTD3-8p-7@gated-at.bofh.it> (permalink)
References	<rkqa6-5dS-5@gated-at.bofh.it> <rkqa6-5dS-13@gated-at.bofh.it> <rkNT3-7pr-9@gated-at.bofh.it> <rlJkm-82k-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On 04/08/2016 12:20 PM, Eric Anholt wrote:
> Stephen Warren <swarren@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@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.

Thread

[PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier call Eric Anholt <eric@anholt.net> - 2016-04-05 05:50 +0200
  Re: [PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier  call Stephen Warren <swarren@wwwdotorg.org> - 2016-04-06 07:10 +0200
    Re: [PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier call Eric Anholt <eric@anholt.net> - 2016-04-08 20:30 +0200
      Re: [PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier  call Stephen Warren <swarren@wwwdotorg.org> - 2016-04-09 07:30 +0200
        Re: [PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier call Eric Anholt <eric@anholt.net> - 2016-04-10 20:40 +0200
          Re: [PATCH 4/4] irqchip: bcm2836: Use a more generic memory barrier  call Stephen Warren <swarren@wwwdotorg.org> - 2016-04-11 18:00 +0200

csiph-web