linux-kernel - Re: [PATCH 2/2] iommu/arm-smmu: Add support for non-coherent page table mappings

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Message-ID: <20190120000117.GH26876@brain-police>
Date:   Sun, 20 Jan 2019 00:01:18 +0000
From:   Will Deacon <will.deacon@....com>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     robin.murphy@....com, joro@...tes.org,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, tfiga@...omium.org
Subject: Re: [PATCH 2/2] iommu/arm-smmu: Add support for non-coherent page
 table mappings

On Thu, Jan 17, 2019 at 02:57:18PM +0530, Vivek Gautam wrote:
> Adding a device tree option for arm smmu to enable non-cacheable
> memory for page tables.
> We already enable a smmu feature for coherent walk based on
> whether the smmu device is dma-coherent or not. Have an option
> to enable non-cacheable page table memory to force set it for
> particular smmu devices.

Hmm, I must be missing something here. What is the difference between this
new property, and simply omitting dma-coherent on the SMMU?

Will