linux-kernel - Re: [PATCH v16 1/5] iommu/arm-smmu: re-enable context caching in smmu reset operation

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Message-ID: <20241024125241.GD30704@willie-the-truck>
Date: Thu, 24 Oct 2024 13:52:42 +0100
From: Will Deacon <will@...nel.org>
To: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
Cc: robdclark@...il.com, robin.murphy@....com, joro@...tes.org,
	jgg@...pe.ca, jsnitsel@...hat.com, robh@...nel.org,
	krzysztof.kozlowski@...aro.org, quic_c_gdjako@...cinc.com,
	dmitry.baryshkov@...aro.org, iommu@...ts.linux.dev,
	linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Konrad Dybcio <konrad.dybcio@...aro.org>
Subject: Re: [PATCH v16 1/5] iommu/arm-smmu: re-enable context caching in
 smmu reset operation

On Tue, Oct 08, 2024 at 06:24:06PM +0530, 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.
> 
> Reviewed-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> Signed-off-by: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
> ---
>  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 45 ++++++++++++++++++++--
>  1 file changed, 42 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 087fb4f6f4d3..0cb10b354802 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> @@ -16,6 +16,16 @@
> 
>  #define QCOM_DUMMY_VAL	-1
> 
> +/*
> + * SMMU-500 TRM defines BIT(0) as CMTLB (Enable context caching in the
> + * macro TLB) and BIT(1) as CPRE (Enable context caching in the prefetch
> + * buffer). The remaining bits are implementation defined and vary across
> + * SoCs.
> + */
> +
> +#define CPRE			(1 << 1)
> +#define CMTLB			(1 << 0)
> +
>  static struct qcom_smmu *to_qcom_smmu(struct arm_smmu_device *smmu)
>  {
>  	return container_of(smmu, struct qcom_smmu, smmu);
> @@ -396,11 +406,40 @@ 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 ret;
> +	u32 val;
> +	int i;
> +
> +	ret = arm_mmu500_reset(smmu);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * arm_mmu500_reset() disables CPRE which is re-enabled here.
> +	 * The errata for MMU-500 before the r2p2 revision requires CPRE to be
> +	 * disabled. The arm_mmu500_reset function disables CPRE to accommodate all
> +	 * RTL revisions. Since all Qualcomm SoCs are on the r2p4 revision, where
> +	 * the CPRE bit can be enabled, the qcom_smmu500_reset function re-enables
> +	 * the CPRE bit for the next-page prefetcher to retain the prefetch value
> +	 * during reset and runtime suspend operations.
> +	 */
> +
> +	for (i = 0; i < smmu->num_context_banks; ++i) {
> +		val = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
> +		val |= CPRE;
> +		arm_smmu_cb_write(smmu, i, ARM_SMMU_CB_ACTLR, val);
> +	}

If CPRE only needs to be disabled prior to r2p2, then please teach the
MMU-500 code about that instead of adding qualcomm-specific logic here.

Will