Re: [PATCHv2 2/2] iommu/arm-smmu-qcom: Move the adreno smmu specific impl earlier

[Jordan Crouse <jordan@cosmicpenguin.net>]

On Fri, Feb 26, 2021 at 11:48:13AM -0700, Jordan Crouse wrote:
> On Fri, Feb 26, 2021 at 11:24:52AM -0600, Bjorn Andersson wrote:
> > On Fri 26 Feb 03:55 CST 2021, Sai Prakash Ranjan wrote:
> > 
> > > Adreno(GPU) SMMU and APSS(Application Processor SubSystem) SMMU
> > > both implement "arm,mmu-500" in some QTI SoCs and to run through
> > > adreno smmu specific implementation such as enabling split pagetables
> > > support, we need to match the "qcom,adreno-smmu" compatible first
> > > before apss smmu or else we will be running apps smmu implementation
> > > for adreno smmu and the additional features for adreno smmu is never
> > > set. For ex: we have "qcom,sc7280-smmu-500" compatible for both apps
> > > and adreno smmu implementing "arm,mmu-500", so the adreno smmu
> > > implementation is never reached because the current sequence checks
> > > for apps smmu compatible(qcom,sc7280-smmu-500) first and runs that
> > > specific impl and we never reach adreno smmu specific implementation.
> > > 
> > 
> > So you're saying that you have a single SMMU instance that's compatible
> > with both an entry in qcom_smmu_impl_of_match[] and "qcom,adreno-smmu"?
> > 
> > Per your proposed change we will pick the adreno ops _only_ for this
> > component, essentially disabling the non-Adreno quirks selected by the
> > qcom impl. As such keeping the non-adreno compatible in the
> > qcom_smmu_impl_init[] seems to only serve to obfuscate the situation.
> > 
> > Don't we somehow need the combined set of quirks? (At least if we're
> > running this with a standard UEFI based boot flow?)
> 
> We *do* need the combined set of quirks, so there has to be an adreno-smmu
> impelmentation that matches the "generic" implementation with a few extra
> function hooks added on. I'm not sure if there is a clever way to figure out how
> to meld the implementation hooks at runtime but the alternative is to just make
> sure that the adreno-smmu static struct calls the same quirks as its generic
> partner.

To clarify, the gpu-smmu doesn't strictly need the s2cr handoff or the cfg_probe
though it wouldn't hurt to have them since they would be essentially
passthroughs for the GPU. We do need to capture errata like the
sdm845_smmu500_reset which is already part of the upstream adreno
implementation.

I think the main takeaway is that if a new errata or quirk is added
for main mmu500 it needs to be considered for adreno-smmu too.

Jordan

> > > Suggested-by: Akhil P Oommen <akhilpo@codeaurora.org>
> > > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> > > ---
> > >  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 12 +++++++++---
> > >  1 file changed, 9 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > index bea3ee0dabc2..03f048aebb80 100644
> > > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > @@ -345,11 +345,17 @@ struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu)
> > >  {
> > >  	const struct device_node *np = smmu->dev->of_node;
> > >  
> > > -	if (of_match_node(qcom_smmu_impl_of_match, np))
> > > -		return qcom_smmu_create(smmu, &qcom_smmu_impl);
> > > -
> > > +	/*
> > > +	 * Do not change this order of implementation, i.e., first adreno
> > > +	 * smmu impl and then apss smmu since we can have both implementing
> > > +	 * arm,mmu-500 in which case we will miss setting adreno smmu specific
> > > +	 * features if the order is changed.
> > > +	 */
> > >  	if (of_device_is_compatible(np, "qcom,adreno-smmu"))
> > >  		return qcom_smmu_create(smmu, &qcom_adreno_smmu_impl);
> > >  
> > > +	if (of_match_node(qcom_smmu_impl_of_match, np))
> > > +		return qcom_smmu_create(smmu, &qcom_smmu_impl);
> > > +
> > >  	return smmu;
> > >  }
> > > -- 
> > > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> > > of Code Aurora Forum, hosted by The Linux Foundation
> > > 
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