linux-kernel - Re: [PATCHv2] iommu/arm-smmu-qcom: Add debug support for TLB sync timeouts

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Message-ID: <20220706115638.GD2403@willie-the-truck>
Date:   Wed, 6 Jul 2022 12:56:39 +0100
From:   Will Deacon <will@...nel.org>
To:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, quic_guptap@...cinc.com,
        Rob Clark <robdclark@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCHv2] iommu/arm-smmu-qcom: Add debug support for TLB sync
 timeouts

On Thu, May 26, 2022 at 09:44:03AM +0530, Sai Prakash Ranjan wrote:
> TLB sync timeouts can be due to various reasons such as TBU power down
> or pending TCU/TBU invalidation/sync and so on. Debugging these often
> require dumping of some implementation defined registers to know the
> status of TBU/TCU operations and some of these registers are not
> accessible in non-secure world such as from kernel and requires SMC
> calls to read them in the secure world. So, add this debug support
> to dump implementation defined registers for TLB sync timeout issues.
> 
> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@...cinc.com>
> ---
> 
> Changes in v2:
>  * Use scm call consistently so that it works on older chipsets where
>    some of these regs are secure registers.
>  * Add device specific data to get the implementation defined register
>    offsets.
> 
> ---
>  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 161 ++++++++++++++++++---
>  drivers/iommu/arm/arm-smmu/arm-smmu.c      |   2 +
>  drivers/iommu/arm/arm-smmu/arm-smmu.h      |   1 +
>  3 files changed, 146 insertions(+), 18 deletions(-)

If this is useful to you, then I suppose it's something we could support,
however I'm pretty worried about our ability to maintain/scale this stuff
as it is extended to support additional SoCs and other custom debugging
features.

Perhaps you could stick it all in arm-smmu-qcom-debug.c and have a new
config option for that, so at least it's even further out of the way?

Will