linux-kernel - Re: [PATCH 1/6] iommu/qcom: Use the asid read from device-tree if specified

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Message-ID: <20220531154631.GA25502@willie-the-truck>
Date:   Tue, 31 May 2022 16:46:31 +0100
From:   Will Deacon <will@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht,
        linux-arm-msm@...r.kernel.org, bjorn.andersson@...aro.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, martin.botka@...ainline.org,
        angelogioacchino.delregno@...ainline.org,
        marijn.suijten@...ainline.org, jamipkettunen@...ainline.org,
        Andy Gross <agross@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Clark <robdclark@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] iommu/qcom: Use the asid read from device-tree if
 specified

On Fri, May 27, 2022 at 11:28:56PM +0200, Konrad Dybcio wrote:
> From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> 
> As specified in this driver, the context banks are 0x1000 apart.
> Problem is that sometimes the context number (our asid) does not
> match this logic and we end up using the wrong one: this starts
> being a problem in the case that we need to send TZ commands
> to do anything on a specific context.

I don't understand this. The ASID is a software construct, so it shouldn't
matter what we use. If it does matter, then please can you explain why? The
fact that the context banks are 0x1000 apart seems unrelated.

Will