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

[Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>]

Hi Mike,

On 2020-08-05 18:24, Mike Leach wrote:
> 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 etm4_count race is a bug fix which in my opinion should go first 
because
this feature would likely to be merged for 5.10 and till then we would 
have
a bug lying around if the fix patch for the race does not go in right?

Thanks,
Sai

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