linux-kernel - Re: [PATCH] iommu/arm-smmu-qcom: Only enable stall on smmu-v2

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Message-ID: <41d93dac-4ef1-4cc7-a7b2-24c8289f905f@arm.com>
Date: Thu, 19 Dec 2024 12:08:39 +0000
From: Robin Murphy <robin.murphy@....com>
To: Will Deacon <will@...nel.org>, Rob Clark <robdclark@...il.com>
Cc: iommu@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
 freedreno@...ts.freedesktop.org, Akhil P Oommen <quic_akhilpo@...cinc.com>,
 Rob Clark <robdclark@...omium.org>, Joerg Roedel <joro@...tes.org>,
 "moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/arm-smmu-qcom: Only enable stall on smmu-v2

On 2024-12-19 11:30 am, Will Deacon wrote:
> On Mon, Dec 16, 2024 at 09:10:17AM -0800, Rob Clark wrote:
>> From: Rob Clark <robdclark@...omium.org>
>>
>> On mmu-500, stall-on-fault seems to stall all context banks, causing the
>> GMU to misbehave.  So limit this feature to smmu-v2 for now.
> 
> MMU-500 has public documentation so please can you dig up what the
> actual behaviour is rather than guess?

Yeah, I'm pretty sure that's not true as stated, especially with 
SCTLR.HUPCF set as qcom_adreno_smmu_write_sctlr() does. However it is 
plausible that at the system interconnect level, a sufficient number of 
stalled transactions might backpressure other transactions from entering 
the same TBU, even if they are destined for a different context. That's 
more about the configuration and integration of individual SoCs than the 
SMMU IP used.

Robin.

>> This fixes an issue with an older mesa bug taking outo the system
>> because of GMU going off into the year.
> 
> Sorry, but I don't understand this sentence.
> 
> Will