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

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Message-ID: <YDku5PFQZetP4iG8@builder.lan>
Date:   Fri, 26 Feb 2021 11:24:52 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCHv2 2/2] iommu/arm-smmu-qcom: Move the adreno smmu specific
 impl earlier

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?)

Regards,
Bjorn

> Suggested-by: Akhil P Oommen <akhilpo@...eaurora.org>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.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;
>  }
> -- 
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>