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

On Thu, Mar 25, 2021 at 01:10:12PM +0530, Sai Prakash Ranjan wrote:

On 2021-03-15 00:31, Sai Prakash Ranjan wrote:

quoted

On 2021-03-12 04:59, Bjorn Andersson wrote:

quoted

On Sat 27 Feb 07:53 CST 2021, Sai Prakash Ranjan wrote:

quoted

On 2021-02-27 00:44, Bjorn Andersson wrote:

quoted

On Fri 26 Feb 12:23 CST 2021, Rob Clark wrote:


The current logic picks one of:
1) is the compatible mentioned in qcom_smmu_impl_of_match[]
2) is the compatible an adreno
3) no quirks needed

The change flips the order of these, so the only way I can see this
change affecting things is if we expected a match on #2, but we got one
on #1.

Which implies that the instance that we want to act according to the
adreno impl was listed in qcom_smmu_impl_of_match[] - which either is
wrong, or there's a single instance that needs both behaviors.

(And I believe Jordan's answer confirms the latter - there's a single
SMMU instance that needs all them quirks at once)

Let me go through the problem statement in case my commit
message wasn't
clear. There are two SMMUs (APSS and GPU) on SC7280 and both are
SMMU500
(ARM SMMU IP).

APSS SMMU compatible - ("qcom,sc7280-smmu-500", "arm,mmu-500")
GPU SMMU compatible - ("qcom,sc7280-smmu-500",
"qcom,adreno-smmu", "arm,mmu-500")

Now if we take SC7180 as an example, GPU SMMU was QSMMU(QCOM SMMU IP)
and APSS SMMU was SMMU500(ARM SMMU IP).

APSS SMMU compatible - ("qcom,sc7180-smmu-500", "arm,mmu-500")
GPU SMMU compatible - ("qcom,sc7180-smmu-v2",
"qcom,adreno-smmu", "qcom,smmu-v2")

Current code sequence without this patch,

if (of_match_node(qcom_smmu_impl_of_match, np))
                 return qcom_smmu_create(smmu, &qcom_smmu_impl);

if (of_device_is_compatible(np, "qcom,adreno-smmu"))
        return qcom_smmu_create(smmu, &qcom_adreno_smmu_impl);

Now if we look at the compatible for SC7180, there is no problem
because
the APSS SMMU will match the one in qcom_smmu_impl_of_match[]
and GPU SMMU
will match "qcom,adreno-smmu" because the compatible strings are
different.
But for SC7280, both the APSS SMMU and GPU SMMU
compatible("qcom,sc7280-smmu-500")
are same. So GPU SMMU will match with the one in
qcom_smmu_impl_of_match[]
i.e.., "qcom,sc7280-smmu-500" which functionally doesn't cause
any problem
but we will miss settings for split pagetables which are part of
GPU SMMU
specific implementation.

We can avoid this with yet another new compatible for GPU SMMU
something like
"qcom,sc7280-adreno-smmu-500" but since we can handle this
easily in the
driver and since the IPs are same, meaning if there was a
hardware quirk
required, then we would need to apply to both of them and would
this additional
compatible be of any help?

No, I think you're doing the right thing of having them both. I just
didn't remember us doing that.

quoted

Coming to the part of quirks now, you are right saying both
SMMUs will need
to have the same quirks in SC7280 and similar others where both
are based on
same IPs but those should probably be *hardware quirks* and if
they are
software based like the S2CR quirk depending on the firmware,
then it might
not be applicable to both. In case if it is applicable, then as
Jordan mentioned,
we can add the same quirks in GPU SMMU implementation.

I do suspect that at some point (probably sooner than later) we'd have
to support both inheriting of stream from the bootloader and the
Adreno
"quirks" in the same instance.

But for now this is okay to me.

Sure, let me know if you or anyone face any issues without it and I will
add it. I will resend this series with the dt-bindings patch for sc7280
smmu
which wasn't cc'd to smmu folks by mistake.

I think there is consensus on this series. I can resend if required but it
still applies cleanly, let me know if you have any comments?

Please resend with the bindings patch, and I'd like Bjorn's Ack as well.

Will

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