Re: [PATCH v2 3/7] coresight: Use event attributes for sink selection

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 01/22/2019 06:11 PM, Mathieu Poirier wrote:
> This patch uses the information conveyed by perf_event::attr::config2
> to select a sink to use for the session.  That way a sink can easily be
> selected to be used by more than one source, something that isn't currently
> possible with the sysfs implementation.
> 
> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> ---
>   .../hwtracing/coresight/coresight-etm-perf.c  | 24 ++++++------
>   drivers/hwtracing/coresight/coresight-priv.h  |  1 +
>   drivers/hwtracing/coresight/coresight.c       | 39 +++++++++++++++++++
>   3 files changed, 52 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index c68a0036532c..ea031eb673b3 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -31,11 +31,14 @@ static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
>   PMU_FORMAT_ATTR(cycacc,		"config:" __stringify(ETM_OPT_CYCACC));
>   PMU_FORMAT_ATTR(timestamp,	"config:" __stringify(ETM_OPT_TS));
>   PMU_FORMAT_ATTR(retstack,	"config:" __stringify(ETM_OPT_RETSTK));
> +/* Sink ID - same for all ETMs */
> +PMU_FORMAT_ATTR(sinkid,		"config2:0-31");
>   
>   static struct attribute *etm_config_formats_attr[] = {
>   	&format_attr_cycacc.attr,
>   	&format_attr_timestamp.attr,
>   	&format_attr_retstack.attr,
> +	&format_attr_sinkid.attr,
>   	NULL,
>   };
>   
> @@ -191,6 +194,7 @@ static void etm_free_aux(void *data)
>   static void *etm_setup_aux(struct perf_event *event, void **pages,
>   			   int nr_pages, bool overwrite)
>   {
> +	u32 id;
>   	int cpu = event->cpu;
>   	cpumask_t *mask;
>   	struct coresight_device *sink;
> @@ -201,18 +205,14 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
>   		return NULL;
>   	INIT_WORK(&event_data->work, free_event_data);
>   
> -	/*
> -	 * In theory nothing prevent tracers in a trace session from being
> -	 * associated with different sinks, nor having a sink per tracer.  But
> -	 * until we have HW with this kind of topology we need to assume tracers
> -	 * in a trace session are using the same sink.  Therefore go through
> -	 * the coresight bus and pick the first enabled sink.
> -	 *
> -	 * When operated from sysFS users are responsible to enable the sink
> -	 * while from perf, the perf tools will do it based on the choice made
> -	 * on the cmd line.  As such the "enable_sink" flag in sysFS is reset.
> -	 */
> -	sink = coresight_get_enabled_sink(true);
> +	/* First get the selected sink from user space. */
> +	if (event->attr.config2) {
> +		id = (u32)event->attr.config2;
> +		sink = coresight_get_sink_by_id(id);
> +	} else {
> +		sink = coresight_get_enabled_sink(true);
> +	}
> +
>   	if (!sink || !sink_ops(sink)->alloc_buffer)
>   		goto err;
>   
> diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> index 579f34943bf1..b936c6d7e13f 100644
> --- a/drivers/hwtracing/coresight/coresight-priv.h
> +++ b/drivers/hwtracing/coresight/coresight-priv.h
> @@ -147,6 +147,7 @@ void coresight_disable_path(struct list_head *path);
>   int coresight_enable_path(struct list_head *path, u32 mode, void *sink_data);
>   struct coresight_device *coresight_get_sink(struct list_head *path);
>   struct coresight_device *coresight_get_enabled_sink(bool reset);
> +struct coresight_device *coresight_get_sink_by_id(u32 id);
>   struct list_head *coresight_build_path(struct coresight_device *csdev,
>   				       struct coresight_device *sink);
>   void coresight_release_path(struct list_head *path);
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index d7fa90be6f42..c5f2df186a19 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -11,6 +11,7 @@
>   #include <linux/err.h>
>   #include <linux/export.h>
>   #include <linux/slab.h>
> +#include <linux/stringhash.h>
>   #include <linux/mutex.h>
>   #include <linux/clk.h>
>   #include <linux/coresight.h>
> @@ -541,6 +542,44 @@ struct coresight_device *coresight_get_enabled_sink(bool deactivate)
>   	return dev ? to_coresight_device(dev) : NULL;
>   }
>   
> +static int coresight_sink_by_id(struct device *dev, void *data)
> +{
> +	struct coresight_device *csdev = to_coresight_device(dev);
> +	u32 hash;
> +
> +	if (csdev->type == CORESIGHT_DEV_TYPE_SINK ||
> +	     csdev->type == CORESIGHT_DEV_TYPE_LINKSINK) {
> +		/*
> +		 * See function etm_perf_sink_name_show() to know where this
> +		 * comes from.
> +		 */
> +		hash = hashlen_hash(hashlen_string(NULL, dev_name(dev)));
> +
> +		if (hash == (*(u32 *)data))
> +			return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * coresight_get_sink_by_id - returns the sink that matches the id
> + * @id: Id of the sink to match
> + *
> + * The name of a sink is unique, whether it is found on the AMBA bus or
> + * otherwise.  As such the hash of that name can easily be used to identify
> + * a sink.
> + */
> +struct coresight_device *coresight_get_sink_by_id(u32 id)
> +{
> +	struct device *dev = NULL;
> +
> +	dev = bus_find_device(&coresight_bustype, NULL, &id,
> +			      coresight_sink_by_id);
> +
> +	return dev ? to_coresight_device(dev) : NULL;
> +}
> +

The patch looks good to me. As mentioned in the previous patch, we may
be able to optimize the look up a bit using dev_ext_attribute. Either
way,

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>