Re: [PATCH v7 09/25] coresight: etm3x: allow etm3x to be built as a module

From: Mike Leach <mike.leach@linaro.org>
To: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: tsoni@codeaurora.org,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
	Kim Phillips <kim.phillips@arm.com>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Coresight ML <coresight@lists.linaro.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	Mian Yousaf Kaukab <ykaukab@suse.de>,
	Russell King <linux@armlinux.org.uk>,
	Mao Jinlong <jinlmao@codeaurora.org>,
	Tingwei Zhang <tingwei@codeaurora.org>,
	Leo Yan <leo.yan@linaro.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v7 09/25] coresight: etm3x: allow etm3x to be built as a module
Date: Wed, 5 Aug 2020 13:54:28 +0100	[thread overview]
Message-ID: <CAJ9a7VjxOPe+s1RN3=2h++4GBG_SSE6H3D5U3eCU+m8DJ_H0kg@mail.gmail.com> (raw)
In-Reply-To: <83abb52f-4c3b-9b50-4053-84343d75eeb3@arm.com>

Hi,

On Wed, 5 Aug 2020 at 12:05, Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
> On 08/05/2020 03:54 AM, Tingwei Zhang wrote:
> > From: Kim Phillips <kim.phillips@arm.com>
> >
> > Allow to build coresight-etm3x as a module, for ease of development.
> >
> > - Kconfig becomes a tristate, to allow =m
> > - append -core to source file name to allow module to
> >    be called coresight-etm3x by the Makefile
> > - add an etm_remove function, for module unload
> > - add a MODULE_DEVICE_TABLE for autoloading on boot
> >
> > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Cc: Leo Yan <leo.yan@linaro.org>
> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> > Cc: Randy Dunlap <rdunlap@infradead.org>
> > Cc: Suzuki K Poulose <Suzuki.Poulose@arm.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Russell King <linux@armlinux.org.uk>
> > Signed-off-by: Kim Phillips <kim.phillips@arm.com>
> > Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>
> > Reviewed-by: Mike Leach <mike.leach@linaro.org>
> > ---
> >   drivers/hwtracing/coresight/Kconfig           |  5 +++-
> >   drivers/hwtracing/coresight/Makefile          |  3 ++-
> >   ...resight-etm3x.c => coresight-etm3x-core.c} | 27 ++++++++++++++++++-
> >   3 files changed, 32 insertions(+), 3 deletions(-)
> >   rename drivers/hwtracing/coresight/{coresight-etm3x.c => coresight-etm3x-core.c} (97%)
> >
> > diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
> > index 6433f835fc97..8fd9fd139cf3 100644
> > --- a/drivers/hwtracing/coresight/Kconfig
> > +++ b/drivers/hwtracing/coresight/Kconfig
> > @@ -65,7 +65,7 @@ config CORESIGHT_SINK_ETBV10
> >         special enhancement or added features.
> >
> >   config CORESIGHT_SOURCE_ETM3X
> > -     bool "CoreSight Embedded Trace Macrocell 3.x driver"
> > +     tristate "CoreSight Embedded Trace Macrocell 3.x driver"
> >       depends on !ARM64
> >       select CORESIGHT_LINKS_AND_SINKS
> >       help
> > @@ -74,6 +74,9 @@ config CORESIGHT_SOURCE_ETM3X
> >         This is primarily useful for instruction level tracing.  Depending
> >         the ETM version data tracing may also be available.
> >
> > +       To compile this driver as a module, choose M here: the
> > +       module will be called coresight-etm3x.
> > +
> >   config CORESIGHT_SOURCE_ETM4X
> >       bool "CoreSight Embedded Trace Macrocell 4.x driver"
> >       depends on ARM64
> > diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
> > index 19497d1d92bf..d619cfd0abd8 100644
> > --- a/drivers/hwtracing/coresight/Makefile
> > +++ b/drivers/hwtracing/coresight/Makefile
> > @@ -11,7 +11,8 @@ obj-$(CONFIG_CORESIGHT_SINK_TPIU) += coresight-tpiu.o
> >   obj-$(CONFIG_CORESIGHT_SINK_ETBV10) += coresight-etb10.o
> >   obj-$(CONFIG_CORESIGHT_LINKS_AND_SINKS) += coresight-funnel.o \
> >                                          coresight-replicator.o
> > -obj-$(CONFIG_CORESIGHT_SOURCE_ETM3X) += coresight-etm3x.o coresight-etm-cp14.o \
> > +obj-$(CONFIG_CORESIGHT_SOURCE_ETM3X) += coresight-etm3x.o
> > +coresight-etm3x-y := coresight-etm3x-core.o coresight-etm-cp14.o \
> >                                       coresight-etm3x-sysfs.o
> >   obj-$(CONFIG_CORESIGHT_SOURCE_ETM4X) += coresight-etm4x.o \
> >                                       coresight-etm4x-sysfs.o
> > diff --git a/drivers/hwtracing/coresight/coresight-etm3x.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> > similarity index 97%
> > rename from drivers/hwtracing/coresight/coresight-etm3x.c
> > rename to drivers/hwtracing/coresight/coresight-etm3x-core.c
> > index bf22dcfd3327..82b333c40006 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm3x.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> > @@ -895,6 +895,23 @@ static int etm_probe(struct amba_device *adev, const struct amba_id *id)
> >       return ret;
> >   }
> >
> > +static int __exit etm_remove(struct amba_device *adev)
> > +{
> > +     struct etm_drvdata *drvdata = dev_get_drvdata(&adev->dev);
> > +
> > +     etm_perf_symlink(drvdata->csdev, false);
> > +
> > +     if (--etm_count == 0) {
>
> Could there be multiple instances of remove running in parallel ? I
> believe we need some sort of a protection here to avoid racing.
>
> Or even better, I would recommend leaving the notifiers registered
> at module_init and removed at the cleanup of the module, just like
> we are doing for etm4x driver, and get rid of this silly scheme.

I would agree that this needs addressing but this is an independent
problem that could be better served by a separate patchset, rather
than add feature creep to this set. The same schema is used in the CTI
driver as well and needs fixing there.

> Like here :
>
> https://lkml.kernel.org/r/20200729051310.18436-1-saiprakash.ranjan@codeaurora.org
>

This conflicts with the init / exit fns created for module loading in
the etm4x part of this set..

A decision needs to be made on which set gets applied first - my view
is that the module set could go first, then a set fixing the PM
registration issues for all three affected drivers to be applied next.

The change to making all the drivers module loadable  provides the
init functions needed to initalise the PM outside the probe functions,
just like the patch mentioned above and makes a change to all three
drivers easy to create.

Regards

Mike
>
> Cheers
> Suzuki

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK

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