linux-kernel - Re: [PATCH v4 2/4] iommu/arm-smmu: Workaround for Marvell Armada-AP806 SoC erratum #582743

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Date:   Thu, 16 Jul 2020 09:24:58 +0200
From:   Tomasz Nowicki <tn@...ihalf.com>
To:     Robin Murphy <robin.murphy@....com>, will@...nel.org,
        joro@...tes.org, gregory.clement@...tlin.com, robh+dt@...nel.org,
        hannah@...vell.com
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        devicetree@...r.kernel.org, catalin.marinas@....com,
        nadavh@...vell.com, linux-arm-kernel@...ts.infradead.org,
        mw@...ihalf.com
Subject: Re: [PATCH v4 2/4] iommu/arm-smmu: Workaround for Marvell
 Armada-AP806 SoC erratum #582743

On 15.07.2020 12:32, Robin Murphy wrote:
> On 2020-07-15 08:06, Tomasz Nowicki wrote:
>> From: Hanna Hawa <hannah@...vell.com>
>>
>> Due to erratum #582743, the Marvell Armada-AP806 can't access 64bit to
>> ARM SMMUv2 registers.
>>
>> Provide implementation relevant hooks:
>> - split the writeq/readq to two accesses of writel/readl.
>> - mask the MMU_IDR2.PTFSv8 fields to not use AArch64 format (but
>> only AARCH32_L) since with AArch64 format 32 bits access is not 
>> supported.
>>
>> Note that most 64-bit registers like TTBRn can be accessed as two 32-bit
>> halves without issue, and AArch32 format ensures that the register writes
>> which must be atomic (for TLBI etc.) need only be 32-bit.
> 
> Thanks Tomasz, this has ended up as clean as I'd hoped it could, and 
> there's still room to come back and play more complicated games later if 
> a real need for AARCH64_64K at stage 2 crops up.

Based on your implementation infrastructure rework, indeed the code 
looks much cleaner :)

> 
> Reviewed-by: Robin Murphy <robin.murphy@....com>
> 

Thanks!

Tomasz