linux-kernel - Re: [PATCH] coresight: etm4x: Add support to disable trace unit power up

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Date:   Fri, 15 May 2020 21:28:39 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Coresight ML <coresight@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Tingwei Zhang <tingwei@...eaurora.org>,
        Leo Yan <leo.yan@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH] coresight: etm4x: Add support to disable trace unit power
 up

Hi Mathieu,

On 2020-05-15 21:21, Mathieu Poirier wrote:
> On Fri, May 15, 2020 at 08:37:13PM +0530, Sai Prakash Ranjan wrote:
>> Hi Mathieu,
>> 
>> On 2020-05-15 20:22, Mathieu Poirier wrote:
>> > On Thu, 14 May 2020 at 12:39, Sai Prakash Ranjan
>> > <saiprakash.ranjan@...eaurora.org> wrote:
>> > >
>> > > Hi Mathieu,
>> > >
>> > > On 2020-05-14 23:30, Mathieu Poirier wrote:
>> > > > Good morning Sai,
>> > > >
>> > > > On Thu, May 14, 2020 at 04:29:15PM +0530, Sai Prakash Ranjan wrote:
>> > > >> From: Tingwei Zhang <tingwei@...eaurora.org>
>> > > >>
>> > > >> On some Qualcomm Technologies Inc. SoCs like SC7180, there
>> > > >> exists a hardware errata where the APSS (Application Processor
>> > > >> SubSystem)/CPU watchdog counter is stopped when ETM register
>> > > >> TRCPDCR.PU=1.
>> > > >
>> > > > Fun stuff...
>> > > >
>> > >
>> > > Yes :)
>> > >
>> > > >> Since the ETMs share the same power domain as
>> > > >> that of respective CPU cores, they are powered on when the
>> > > >> CPU core is powered on. So we can disable powering up of the
>> > > >> trace unit after checking for this errata via new property
>> > > >> called "qcom,tupwr-disable".
>> > > >>
>> > > >> Signed-off-by: Tingwei Zhang <tingwei@...eaurora.org>
>> > > >> Co-developed-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> > > >> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> > > >
>> > > > Co-developed-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> > > > Signed-off-by: Tingwei Zhang <tingwei@...eaurora.org>
>> > > >
>> > >
>> > > Tingwei is the author, so if I understand correctly, his signed-off-by
>> > > should appear first, am I wrong?
>> >
>> > It's a gray area and depends on who's code is more prevalent in the
>> > patch.  If Tingwei wrote the most of the code then his name is in the
>> > "from:" section, yours as co-developer and he signs off on it (as I
>> > suggested).  If you did most of the work then it is the opposite.
>> > Adding a Co-developed and a signed-off with the same name doesn't make
>> > sense.
>> >
>> 
>> I did check the documentation for submitting patches:
>> Documentation/process/submitting-patches.rst. And it clearly states
>> that "Co-developed-by must be followed by Signed-off by the co-author
>> and the last Signed-off-by: must always be that of the developer
>> submitting the patch".
>> 
>> Quoting below from the doc:
>> 
>> Co-developed-by: <snip> ...Since
>> Co-developed-by: denotes authorship, every Co-developed-by: must be
>> immediately
>> followed by a Signed-off-by: of the associated co-author.  Standard 
>> sign-off
>> procedure applies, i.e. the ordering of Signed-off-by: tags should 
>> reflect
>> the
>> chronological history of the patch insofar as possible, regardless of
>> whether
>> the author is attributed via From: or Co-developed-by:.  Notably, the 
>> last
>> Signed-off-by: must always be that of the developer submitting the 
>> patch.
> 
> Ah yes, glad to see that got clarified.  You can ignore my 
> recommendation on
> that snippet.
> 
>> 
>> > >
>> > > >> ---
>> > > >>  .../devicetree/bindings/arm/coresight.txt     |  6 ++++
>> > > >>  drivers/hwtracing/coresight/coresight-etm4x.c | 29
>> > > >> ++++++++++++-------
>> > > >
>> > > > Please split in two patches.
>> > > >
>> > >
>> > > Sure, I will split the dt-binding into separate patch, checkpatch did
>> > > warn.
>> >
>> > And you still sent me the patch...  I usually run checkpatch before
>> > all the submissions I review and flatly ignore patches that return
>> > errors.  You got lucky...
>> >
>> 
>> I did not mean to ignore it or else I wouldn't have run checkpatch 
>> itself.
>> I checked other cases like "arm,scatter-gather" where the binding and 
>> the
>> driver change was in a single patch, hence I thought it's not a very 
>> strict
>> rule.
> 
> The patch has another warning for a line over 80 characters, that 
> should have
> been fixed before sending.  Putting DT changes in a separate patch is 
> always
> better for the DT people.  They review tons of patches and making their 
> life
> easier is always a good thing.
> 

Ok, I will fix this and resend. I did not want to change it in case if 
it affects
readability since most maintainers prefer to ignore this 80 characters 
warning if
it affects readability. I will keep this in mind for future patches as 
well.

Thanks,
Sai
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