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

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Message-ID: <CAF6AEGsFeibyH5_a7m=9PMKReD4Xb+c=dEGsbCN0_UHiJK1vbA@mail.gmail.com>
Date: Mon, 16 Dec 2024 12:54:43 -0800
From: Rob Clark <robdclark@...il.com>
To: Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc: iommu@...ts.linux.dev, linux-arm-msm@...r.kernel.org, 
	freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...omium.org>, 
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>, 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 Mon, Dec 16, 2024 at 12:28 PM Akhil P Oommen
<quic_akhilpo@...cinc.com> wrote:
>
> On 12/16/2024 10:40 PM, 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.
> >
> > This fixes an issue with an older mesa bug taking outo the system
> > because of GMU going off into the year.
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > index c4c52f7bd09a..1c881e88fc4d 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > @@ -331,8 +331,10 @@ static int qcom_adreno_smmu_init_context(struct arm_smmu_domain *smmu_domain,
> >       priv->get_ttbr1_cfg = qcom_adreno_smmu_get_ttbr1_cfg;
> >       priv->set_ttbr0_cfg = qcom_adreno_smmu_set_ttbr0_cfg;
> >       priv->get_fault_info = qcom_adreno_smmu_get_fault_info;
> > -     priv->set_stall = qcom_adreno_smmu_set_stall;
> > -     priv->resume_translation = qcom_adreno_smmu_resume_translation;
> > +     if (of_device_is_compatible(np, "qcom,smmu-v2")) {
> > +             priv->set_stall = qcom_adreno_smmu_set_stall;
> > +             priv->resume_translation = qcom_adreno_smmu_resume_translation;
> > +     }
>
> Shall we disable this from the driver instead? A debugfs knob to trigger
> coredump after a pagefault is very convenient.

It would require the driver to find the compatible for the smmu, so it
could differentiate btwn smmu-v2 and mmu-500, which seemed like it
might be a bit uglier.

Ideally/hopefully we could figure out how to make GMU a bit more
resilient in the face of stalled translations, because it is useful to
get accurate devcore dumps on smmu faults.  At that point we could
revert this change.

BR,
-R

>
> -Akhil
>
> >       priv->set_prr_bit = NULL;
> >       priv->set_prr_addr = NULL;
> >
>