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

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Date:   Fri, 15 May 2020 09:51:44 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.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

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.

Regards,
Mathieu

> 
> Thanks,
> Sai
> -- 
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