linux-kernel - Re: [PATCH] coresight: etm4x: Skip setting LPOVERRIDE bit for qcom,skip-power-up

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Message-ID: <9e19d312-9de4-2ed8-75ca-c774b93bfe11@arm.com>
Date:   Fri, 16 Oct 2020 14:15:58 +0100
From:   Suzuki Poulose <suzuki.poulose@....com>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>, coresight@...ts.linaro.org,
        Stephen Boyd <swboyd@...omium.org>, denik@...omium.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] coresight: etm4x: Skip setting LPOVERRIDE bit for
 qcom,skip-power-up

On 10/16/20 12:47 PM, Sai Prakash Ranjan wrote:
> Hi Suzuki,
> 
> On 2020-10-16 16:51, Suzuki Poulose wrote:
>> Hi Sai,
>>
>> On 10/16/20 11:10 AM, Sai Prakash Ranjan wrote:
>>> There is a bug on the systems supporting to skip power up
>>> (qcom,skip-power-up) where setting LPOVERRIDE bit(low-power
>>> state override behaviour) will result in CPU hangs/lockups
>>> even on the implementations which supports it. So skip
>>> setting the LPOVERRIDE bit for such platforms.
>>>
>>> Fixes: 02510a5aa78d ("coresight: etm4x: Add support to skip trace 
>>> unit power up")
>>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>>
>> The fix is fine by me. Btw, is there a hardware Erratum assigned for
>> this ? It would be good to have the Erratum documented somewhere,
>> preferrably ( Documentation/arm64/silicon-errata.rst )
>>
> 
> No, afaik we don't have any erratum assigned to this bug.

Ok. Please double check, if there are any.

> It was already present in downstream kernel and since we
> support these targets with the previous HW bug
> (qcom,skip-power-up) now in upstream, we would need this
> fix in upstream kernel as well.

I understand the need for the fix and we must fix it. I was
looking to document this in the central place for errata's
handled in the kernel. And I missed asking this question
when the original patch was posted. So, thought of asking
the question now anyways. Better late than never ;-)

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>