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Subject: Re: [PATCH] coresight: etm4x: Skip setting LPOVERRIDE bit for
 qcom,skip-power-up
To:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc:     Mathieu Poirier <mathieu.poirier@linaro.org>,
        Mike Leach <mike.leach@linaro.org>, coresight@lists.linaro.org,
        Stephen Boyd <swboyd@chromium.org>, denik@chromium.org,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
References: <20201016101025.26505-1-saiprakash.ranjan@codeaurora.org>
 <5c4f6f5d-b07d-0816-331f-7c7463fa99b3@arm.com>
 <41bbcd43c2b016b6d785c3750622e9fe@codeaurora.org>
From:   Suzuki Poulose <suzuki.poulose@arm.com>
Message-ID: <9e19d312-9de4-2ed8-75ca-c774b93bfe11@arm.com>
Date:   Fri, 16 Oct 2020 14:15:58 +0100
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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@codeaurora.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@arm.com>