Re: [PATCH v8 09/24] coresight: etm3x: allow etm3x to be built as a module

From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: tingwei@codeaurora.org, mathieu.poirier@linaro.org,
	alexander.shishkin@linux.intel.com, mike.leach@linaro.org
Cc: tsoni@codeaurora.org, saiprakash.ranjan@codeaurora.org,
	kim.phillips@arm.com, jinlmao@codeaurora.org,
	gregkh@linuxfoundation.org, coresight@lists.linaro.org,
	rdunlap@infradead.org, ykaukab@suse.de, linux@armlinux.org.uk,
	leo.yan@linaro.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v8 09/24] coresight: etm3x: allow etm3x to be built as a module
Date: Thu, 13 Aug 2020 10:47:22 +0100	[thread overview]
Message-ID: <375f5a93-aa4e-14c0-33d6-af4894375986@arm.com> (raw)
In-Reply-To: <20200807111153.7784-10-tingwei@codeaurora.org>

On 08/07/2020 12:11 PM, 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) {
> +		cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
> +		if (hp_online)
> +			cpuhp_remove_state_nocalls(hp_online);
> +	}
> +

As mentioned in the previous version, this needs fixing
similar to the etm4x to avoid races with etm_count. I understand
that it is an exisiting problem. But this set exposes it more
due to etm_remove() calls and is much more probable to hit it.

Suzuki

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