linux-kernel - Re: [PATCH v2 2/2] arm64: dts: qcom: sc8280xp: Describe the PCIe SMMUv3

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Message-ID: <b9724b4c-7c99-4903-aa53-19592df5695f@linaro.org>
Date: Mon, 18 Mar 2024 10:21:13 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
 Rob Herring <robh@...nel.org>, Marijn Suijten
 <marijn.suijten@...ainline.org>, linux-arm-msm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
 Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH v2 2/2] arm64: dts: qcom: sc8280xp: Describe the PCIe
 SMMUv3

On 18.03.2024 02:31, Bjorn Andersson wrote:
> On Sat, Mar 09, 2024 at 02:31:10PM +0100, Konrad Dybcio wrote:
>> SC8280XP actually has a third SMMU, which can be seen in e.g. the IORT
>> ACPI table and is used for the PCIe hosts.
>>
>> Unfortunately though, the secure firmware seems to be configured in a
>> way such that Linux can't touch it, not even read back the ID registers.
>> It also seems like the SMMU is configured to run in some sort of bypass
>> mode, completely opaque to the OS.
>>
>> Describe it so that one can configure it when running Linux as a
>> hypervisor (e.g with [1]) and for hardware description completeness.
>>
>> [1] https://github.com/TravMurav/slbounce
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> 
> Have this information been validated? Or are you suggesting we add it
> for documentation purposes?

I confirmed the platforms boots up with this if the hypervisor is gone.

Konrad