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

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Date:   Thu, 7 Jul 2022 11:50:15 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Will Deacon <will@...nel.org>
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 7/6/2022 5:26 PM, Will Deacon wrote:
> 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

Sounds good to me, will do that.

Thanks,
Sai