linux-kernel - Re: [PATCH v3 04/13] coresight: etm4x: Update ETM4 driver to use Trace ID API

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Message-ID: <01570ba2-81c9-e4b5-6669-0e4087a4bd1f@arm.com>
Date:   Mon, 3 Oct 2022 10:31:47 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Mike Leach <mike.leach@...aro.org>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     mathieu.poirier@...aro.org, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, linux-perf-users@...r.kernel.org,
        leo.yan@...aro.org, quic_jinlmao@...cinc.com
Subject: Re: [PATCH v3 04/13] coresight: etm4x: Update ETM4 driver to use
 Trace ID API

On 09/08/2022 23:33, Mike Leach wrote:
> The trace ID API is now used to allocate trace IDs for ETM4.x / ETE
> devices.
> 
> For perf sessions, these will be allocated on enable, and released on
> disable.
> 
> For sysfs sessions, these will be allocated on enable, but only released
> on reset. This allows the sysfs session to interrogate the Trace ID used
> after the session is over - maintaining functional consistency with the
> previous allocation scheme.
> 
> The trace ID will also be allocated on read of the mgmt/trctraceid file.
> This ensures that if perf or sysfs read this before enabling trace, the
> value will be the one used for the trace session.
> 
> Trace ID initialisation is removed from the _probe() function.
> 
> Signed-off-by: Mike Leach <mike.leach@...aro.org>
> ---
>   .../coresight/coresight-etm4x-core.c          | 79 +++++++++++++++++--
>   .../coresight/coresight-etm4x-sysfs.c         | 27 ++++++-
>   drivers/hwtracing/coresight/coresight-etm4x.h |  3 +
>   3 files changed, 100 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index cf249ecad5a5..b4fb28ce89fd 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -42,6 +42,7 @@
>   #include "coresight-etm4x-cfg.h"
>   #include "coresight-self-hosted-trace.h"
>   #include "coresight-syscfg.h"
> +#include "coresight-trace-id.h"
>   
>   static int boot_enable;
>   module_param(boot_enable, int, 0444);
> @@ -234,6 +235,50 @@ static int etm4_trace_id(struct coresight_device *csdev)
>   	return drvdata->trcid;
>   }
>   
> +int etm4_read_alloc_trace_id(struct etmv4_drvdata *drvdata)
> +{
> +	int trace_id;
> +
> +	/*
> +	 * This will allocate a trace ID to the cpu,
> +	 * or return the one currently allocated.
> +	 */
> +	/* trace id function has its own lock */
> +	trace_id = coresight_trace_id_get_cpu_id(drvdata->cpu);
> +	if (IS_VALID_ID(trace_id))
> +		drvdata->trcid = (u8)trace_id;
> +	else
> +		dev_err(&drvdata->csdev->dev,
> +			"Failed to allocate trace ID for %s on CPU%d\n",
> +			dev_name(&drvdata->csdev->dev), drvdata->cpu);
> +	return trace_id;
> +}
> +
> +static int etm4_set_current_trace_id(struct etmv4_drvdata *drvdata)
> +{
> +	int trace_id;
> +
> +	/*
> +	 * Set the currently allocated trace ID - perf allocates IDs
> +	 * as part of setup_aux for all CPUs it may use.
> +	 */
> +	trace_id = coresight_trace_id_read_cpu_id(drvdata->cpu);
> +	if (IS_VALID_ID(trace_id)) {
> +		drvdata->trcid = (u8)trace_id;
> +		return 0;
> +	}
> +
> +	dev_err(&drvdata->csdev->dev, "Failed to set trace ID for %s on CPU%d\n",
> +		dev_name(&drvdata->csdev->dev), drvdata->cpu);
> +
> +	return -EINVAL;
> +}


> +
> +void etm4_release_trace_id(struct etmv4_drvdata *drvdata)
> +{
> +	coresight_trace_id_put_cpu_id(drvdata->cpu);
> +}
> +
>   struct etm4_enable_arg {
>   	struct etmv4_drvdata *drvdata;
>   	int rc;
> @@ -729,6 +774,15 @@ static int etm4_enable_perf(struct coresight_device *csdev,
>   	ret = etm4_parse_event_config(csdev, event);
>   	if (ret)
>   		goto out;
> +
> +	/*
> +	 * perf allocates cpu ids as part of setup - device needs to use
> +	 * the allocated ID.
> +	 */
> +	ret = etm4_set_current_trace_id(drvdata);

So, when do we allocate an id in perf mode ? As far as I can see, this
should be the same as etm4_read_alloc_trace_id() ? Why are they any
different ?

> +	if (ret < 0)
> +		goto out;
> +
>   	/* And enable it */
>   	ret = etm4_enable_hw(drvdata);
>   
> @@ -753,6 +807,11 @@ static int etm4_enable_sysfs(struct coresight_device *csdev)
>   
>   	spin_lock(&drvdata->spinlock);
>   
> +	/* sysfs needs to read and allocate a trace ID */
> +	ret = etm4_read_alloc_trace_id(drvdata);
> +	if (ret < 0)
> +		goto unlock_sysfs_enable;
> +
>   	/*
>   	 * Executing etm4_enable_hw on the cpu whose ETM is being enabled
>   	 * ensures that register writes occur when cpu is powered.
> @@ -764,6 +823,11 @@ static int etm4_enable_sysfs(struct coresight_device *csdev)
>   		ret = arg.rc;
>   	if (!ret)
>   		drvdata->sticky_enable = true;
> +
> +	if (ret)
> +		etm4_release_trace_id(drvdata);
> +
> +unlock_sysfs_enable:
>   	spin_unlock(&drvdata->spinlock);
>   
>   	if (!ret)
> @@ -895,6 +959,8 @@ static int etm4_disable_perf(struct coresight_device *csdev,
>   	/* TRCVICTLR::SSSTATUS, bit[9] */
>   	filters->ssstatus = (control & BIT(9));
>   
> +	/* The perf event will release trace ids when it is destroyed */
> +

At this patch level, there is no release of trace id ? Is that missed in
this patch ? Or am I missing something ?

Suzuki