linux-kernel - Re: [PATCH v4 5/5] iommu/arm-smmu: re-enable context caching in smmu reset operation

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Date: Sat, 16 Dec 2023 00:54:52 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Bibek Kumar Patro <quic_bibekkum@...cinc.com>, will@...nel.org,
 robin.murphy@....com, joro@...tes.org, dmitry.baryshkov@...aro.org,
 jsnitsel@...hat.com, quic_bjorande@...cinc.com, mani@...nel.org,
 quic_eberman@...cinc.com, robdclark@...omium.org,
 u.kleine-koenig@...gutronix.de, robh@...nel.org, vladimir.oltean@....com,
 quic_pkondeti@...cinc.com, quic_molvera@...cinc.com
Cc: linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 qipl.kernel.upstream@...cinc.com
Subject: Re: [PATCH v4 5/5] iommu/arm-smmu: re-enable context caching in smmu
 reset operation

On 15.12.2023 11:18, Bibek Kumar Patro wrote:
> Default MMU-500 reset operation disables context caching in
> prefetch buffer. It is however expected for context banks using
> the ACTLR register to retain their prefetch value during reset
> and runtime suspend.
> 
> Replace default MMU-500 reset operation with Qualcomm specific reset
> operation which envelope the default reset operation and re-enables
> context caching in prefetch buffer for Qualcomm SoCs.
> 
> Signed-off-by: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
> ---
This probably deserves a fixes tag, but I can't find a good commit for
it, so I guess not having it is fine as well.

Also, since it seems to be independent from the rest of the patches, please
reorder it to become patch 1 in the next spin, so that it can perhaps be
easily picked up independently of the rest.

>  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 23 +++++++++++++++++++---
>  1 file changed, 20 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 c8f5dd4186b7..70d2a5d43993 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> @@ -516,11 +516,28 @@ static int qcom_smmu_def_domain_type(struct device *dev)
>  	return match ? IOMMU_DOMAIN_IDENTITY : 0;
>  }
> 
> +static int qcom_smmu500_reset(struct arm_smmu_device *smmu)
> +{
> +	int i;
> +	u32 reg;
That's rather nitty/codestyle-y, but:

- reverse Christmas tree would be nice (it's in a week! :D)
- "reg" to me sounds like "register address", "val" is used widely for
  register values

> +
> +	arm_mmu500_reset(smmu);
We should check the return value here, in case the function is modified
some day in a way that makes it return something else than 0

LGTM otherwise!

Konrad