linux-kernel - Re: [PATCH v2 0/4] Add trace events for SD registers.

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Message-ID: <20190424153115.GA186956@google.com>
Date:   Wed, 24 Apr 2019 09:31:15 -0600
From:   Raul Rangel <rrangel@...omium.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        linux-trace-devel@...r.kernel.org,
        Daniel Kurtz <djkurtz@...omium.org>, zwisler@...omium.org,
        Steven Rostedt <rostedt@...dmis.org>,
        hongjiefang <hongjiefang@...micro.com>,
        Jennifer Dahm <jennifer.dahm@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Kyle Roeschley <kyle.roeschley@...com>,
        Avri Altman <avri.altman@....com>,
        Simon Horman <horms+renesas@...ge.net.au>,
        Raul Rangel <rrangel@...omium.org>
Subject: Re: [PATCH v2 0/4] Add trace events for SD registers.

On Tue, Apr 23, 2019 at 08:29:15AM +0200, Ulf Hansson wrote:
> On Tue, 16 Apr 2019 at 20:33, Raul E Rangel <rrangel@...omium.org> wrote:
> >
> > I am not able to make a single event class for all these registers. They
> > all have different struct sizes and different printf formats.
> >
> > Thanks for the reviews!
> >
> > Changes in v2:
> > - Made trace_sd_scr print out flags.
> > - Add BUILD_BUG_ON to make sure tracing stays in sync with structs.
> > - memcpy using sizeof(__entry->raw)
> >
> > Raul E Rangel (4):
> >   mmc: core: Add trace event for SD SCR response
> >   mmc: core: Add trace event for SD SSR response
> >   mmc: core: Add trace event for SD OCR response
> >   mmc: core: Add trace event for CSD response
> >
> >  drivers/mmc/core/mmc.c     |   4 +
> >  drivers/mmc/core/sd.c      |  10 ++
> >  drivers/mmc/core/sd_ops.c  |   6 ++
> >  include/trace/events/mmc.h | 204 +++++++++++++++++++++++++++++++++++++
> >  4 files changed, 224 insertions(+)
> >
> > --
> > 2.21.0.392.gf8f6787159e-goog
> >
> 
> Why do you need this? We already have these card registers reflected
> though sysfs files, isn't that sufficient?
> 
I was not actually aware that the registers were exposed via sysfs. I
was debugging a problem where the host controller was returning all
zeros when reading from the card. I wasn't aware that it was returning
all zeros until I added tracing. It made it quite easy to diagnose the
problem by just diffing the two traces.

Also if the card fails to mount because the data is invalid, the
registers would not be exposed via sysfs. So tracing makes gives us an
easy way to debug these types of failures.

Thanks,
Raul
> Kind regards
> Uffe