linux-kernel - Re: [PATCH 1/1] iommu/arm-smmu: Implement qcom,skip-init

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Date:   Tue, 21 Jul 2020 17:04:11 +0200
From:   Konrad Dybcio <konradybcio@...il.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Will Deacon <will@...nel.org>, skrzynka@...radybcio.pl,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jcrouse@...eaurora.org, John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 1/1] iommu/arm-smmu: Implement qcom,skip-init

So.. is this a no-no?

I of course would like to omit this entirely, but SMMUs on sdm630 and
friends are REALLY picky.. What seems to happen is that when the
driver tries to do things the "standard" way, hypervisor decides to
hang the platform or force a reboot. Not very usable.

This thing is needed for the platform to even boot properly and one
more [1] is required to make mdss work with video mode panels (the
fact that CMD-mode panels work is kinda hilarious to me).

To be honest, there are even more qcom quirks (of which at least
qcom,dynamic and qcom-use-3-lvl-tables are used on 630).. [2]

Looking forward to your answers and possibly better solutions.

[1] https://github.com/konradybcio/linux/commit/83ac38af259968f92b6a8b7eab90096c78469f87
[2] https://github.com/sonyxperiadev/kernel/blob/aosp/LA.UM.7.1.r1/drivers/iommu/arm-smmu.c#L404-L415

Regards
Konrad