linux-kernel - Re: [PATCH v7 2/7] iommu/arm-smmu-qcom-tbu: Add Qualcomm TBU driver

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Date: Tue, 9 Apr 2024 11:20:33 +0100
From: Will Deacon <will@...nel.org>
To: Georgi Djakov <quic_c_gdjako@...cinc.com>
Cc: robin.murphy@....com, joro@...tes.org, iommu@...ts.linux.dev,
	robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org, devicetree@...r.kernel.org,
	andersson@...nel.org, konrad.dybcio@...aro.org, robdclark@...il.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, quic_cgoldswo@...cinc.com,
	quic_sukadev@...cinc.com, quic_pdaly@...cinc.com,
	quic_sudaraja@...cinc.com, djakov@...nel.org
Subject: Re: [PATCH v7 2/7] iommu/arm-smmu-qcom-tbu: Add Qualcomm TBU driver

On Fri, Mar 29, 2024 at 02:06:33PM -0700, Georgi Djakov wrote:
> Operating the TBUs (Translation Buffer Units) from Linux on Qualcomm
> platforms can help with debugging context faults. To help with that,
> the TBUs can run ATOS (Address Translation Operations) to manually
> trigger address translation of IOVA to physical address in hardware
> and provide more details when a context fault happens.
> 
> The driver will control the resources needed by the TBU to allow
> running the debug operations such as ATOS, check for outstanding
> transactions, do snapshot capture etc.
> 
> Signed-off-by: Georgi Djakov <quic_c_gdjako@...cinc.com>
> ---
>  drivers/iommu/Kconfig                         |   9 +
>  drivers/iommu/arm/arm-smmu/Makefile           |   1 +
>  .../iommu/arm/arm-smmu/arm-smmu-qcom-tbu.c    | 372 ++++++++++++++++++
>  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.h    |   2 +
>  drivers/iommu/arm/arm-smmu/arm-smmu.h         |   2 +
>  5 files changed, 386 insertions(+)
>  create mode 100644 drivers/iommu/arm/arm-smmu/arm-smmu-qcom-tbu.c
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 0af39bbbe3a3..b699e88f42c5 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -374,6 +374,15 @@ config ARM_SMMU_QCOM
>  	  When running on a Qualcomm platform that has the custom variant
>  	  of the ARM SMMU, this needs to be built into the SMMU driver.
>  
> +config ARM_SMMU_QCOM_TBU
> +	bool "Qualcomm TBU driver"
> +	depends on ARM_SMMU_QCOM
> +	help
> +	  The SMMUs on Qualcomm platforms may include Translation Buffer
> +	  Units (TBUs) for each master. Enabling support for these units
> +	  allows to operate the TBUs and obtain additional information
> +	  when debugging memory management issues like context faults.
> +
>  config ARM_SMMU_QCOM_DEBUG

Can we just use ARM_SMMU_QCOM_DEBUG for all of this? Having both
ARM_SMMU_QCOM_DEBUG and ARM_SMMU_QCOM_TBU for the same hardware is
pretty confusing, I think.

Will