linux-kernel - Re: [PATCH] iommu/arm-smmu-qcom: Enable use of all SMR groups when running bare-metal

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Message-Id: <176408774799.1871149.15645186594285769855.b4-ty@kernel.org>
Date: Tue, 25 Nov 2025 18:05:40 +0000
From: Will Deacon <will@...nel.org>
To: Robin Murphy <robin.murphy@....com>,
	Joerg Roedel <joro@...tes.org>,
	Stephan Gerhold <stephan.gerhold@...aro.org>
Cc: catalin.marinas@....com,
	kernel-team@...roid.com,
	Will Deacon <will@...nel.org>,
	Rob Clark <robin.clark@....qualcomm.com>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Johan Hovold <johan@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	iommu@...ts.linux.dev,
	linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu-qcom: Enable use of all SMR groups when running bare-metal

On Thu, 21 Aug 2025 10:33:53 +0200, Stephan Gerhold wrote:
> Some platforms (e.g. SC8280XP and X1E) support more than 128 stream
> matching groups. This is more than what is defined as maximum by the ARM
> SMMU architecture specification. Commit 122611347326 ("iommu/arm-smmu-qcom:
> Limit the SMR groups to 128") disabled use of the additional groups because
> they don't exhibit the same behavior as the architecture supported ones.
> 
> It seems like this is just another quirk of the hypervisor: When running
> bare-metal without the hypervisor, the additional groups appear to behave
> just like all others. The boot firmware uses some of the additional groups,
> so ignoring them in this situation leads to stream match conflicts whenever
> we allocate a new SMR group for the same SID.
> 
> [...]

Applied to iommu (arm/smmu/updates), thanks!

[1/1] iommu/arm-smmu-qcom: Enable use of all SMR groups when running bare-metal
      https://git.kernel.org/iommu/c/5583a55e074b

I chatted off-list with Robin about this and we agreed that it's the best
approach for now.

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev