linux-kernel - Re: Coresight etmv4 enable over 32bit kernel

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Date:   Tue, 11 Dec 2018 17:11:02 +0800
From:   Lei Wen <adrian.wenl@...il.com>
To:     mathieu.poirier@...aro.org
Cc:     linux-kernel@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        leiwen@...look.com
Subject: Re: Coresight etmv4 enable over 32bit kernel

On Tue, Dec 11, 2018 at 2:02 AM Mathieu Poirier
<mathieu.poirier@...aro.org> wrote:
>
> Good day Adrian,
>
> On Sat, 8 Dec 2018 at 05:05, Lei Wen <adrian.wenl@...il.com> wrote:
> >
> > Hi Mathieu,
> >
> > I am enabling etmv4 coresight over one Cortex-A7 soc, using 32bit kernel.
> > And I am following [1] to do experiment regarding the addr_range feature.
>
> That wiki is very old and after reading it again I seriously consider
> removing it.  It is still accurate but there are better ways to do
> things now, i.e perf.  The main openCSD documentation page [2]
> contains everything you need to know about the integration with perf.
>
> [2]. https://github.com/Linaro/OpenCSD/blob/master/HOWTO.md
>
> > The default addr_range is set as _stext~_etext, and it works fine with
> > etb as sink,
> > and etm as source. I could see there are valid kernel addresses using OpenCSD.
>
> I'm really curious about how you use openCSD to validate your traces -
> can you  expand more on that?


I just manually replace the cstrace.bin in the
decoder/tests/snapshots/juno-ret-stck/.
And modify the register data according to my platform.
Then produce the decode result by below command:
./decoder/tests/bin/builddir/trc_pkt_lister -ss_dir
decoder/tests/snapshots/test -decode -logfilename 2.ppl

>
> I think the results are misleading you since the openCSD library can't
> readily be used to decode sysfs trace sessions.  The wiki doesn't
> mention using openCSD to decode traces either.  The only integrated
> way to use openCSD to decode CoreSight traces is via perf.  Again, the
> link above will give you all the information you need to do that.

>
> >
> > But while I try to store one small range of address pair, which contain only one
> > kernel function. It doesn't behavior like what said in [1], the write
> > pointer would
> > grows rapidly with the read pointer. And I dump the etb buffer and parse it with
> > openCSD, finding that there is no I_ASYNC packet in the dump and is fulled with
> > I_NOT_SYNC.
> >
> > So my question is why ETB continue to grow when there is no trigger at all?
> > Is it normal? I could provide more info if you need it.
>
> I am dubious about the validation process and as such can't comment on
> this.  Please share your results using the perf integration and then
> I'll be able to have a better idea of what is going on.

I see... I would try use perf to get more result and get back here.

>
> Taking a step back I am curious about the ETMv4/ETB combination...  Is
> the ETB the only sink you have to work with?  Moreover, are you sure
> it is not a TMC-ETF?  The ETMv4/ETB match seems a little odd to me
> since they belong to two different era of the CoreSight architecture.
> Usually with an ETMv4 we will see a TMC-ETR, which as a lot more
> capabilities.

ETR is supported. I use ETB as it is mentioned in that old wiki page.

Thanks,
Lei