linux-kernel - Re: [PATCH 04/11] rvtrace: Add functions to start/stop tracing on a component path

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Message-ID: <20edc3a9-2efe-4431-b198-f00b3940777c@gmail.com>
Date: Wed, 8 Oct 2025 02:13:55 -0700
From: Bo Gan <ganboing@...il.com>
To: Anup Patel <apatel@...tanamicro.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Greg KH <gregkh@...uxfoundation.org>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Ian Rogers <irogers@...gle.com>
Cc: Alexandre Ghiti <alex@...ti.fr>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Jiri Olsa <jolsa@...nel.org>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Liang Kan <kan.liang@...ux.intel.com>, Mayuresh Chitale
 <mchitale@...il.com>, Anup Patel <anup@...infault.org>,
 Atish Patra <atish.patra@...ux.dev>, Andrew Jones <ajones@...tanamicro.com>,
 Sunil V L <sunilvl@...tanamicro.com>, linux-riscv@...ts.infradead.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 Mayuresh Chitale <mchitale@...tanamicro.com>
Subject: Re: [PATCH 04/11] rvtrace: Add functions to start/stop tracing on a
 component path

On 10/1/25 23:07, Anup Patel wrote:
> From: Mayuresh Chitale <mchitale@...tanamicro.com>
> 
> The perf driver framework needs to be able to start / stop all components
> in a trace component path during its operation. Add rvtrace_path_start()
> and rvtrace_path_stop() functions for this purpose.
> 
> Co-developed-by: Anup Patel <apatel@...tanamicro.com>
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> Signed-off-by: Mayuresh Chitale <mchitale@...tanamicro.com>
> ---
>   drivers/hwtracing/rvtrace/rvtrace-core.c | 44 ++++++++++++++++++++++++
>   include/linux/rvtrace.h                  |  6 ++++
>   2 files changed, 50 insertions(+)
> 
> diff --git a/drivers/hwtracing/rvtrace/rvtrace-core.c b/drivers/hwtracing/rvtrace/rvtrace-core.c
> index 7013d50ca569..109be40d4b24 100644
> --- a/drivers/hwtracing/rvtrace/rvtrace-core.c
> +++ b/drivers/hwtracing/rvtrace/rvtrace-core.c
> @@ -614,6 +614,50 @@ static void rvtrace_release_path_nodes(struct rvtrace_path *path)
>   	}
>   }
>   
> +int rvtrace_path_start(struct rvtrace_path *path)
> +{
> +	const struct rvtrace_driver *rtdrv;
> +	struct rvtrace_component *comp;
> +	struct rvtrace_path_node *node;
> +	int ret;
> +
> +	list_for_each_entry(node, &path->comp_list, head) {
> +		comp = node->comp;
> +		rtdrv = to_rvtrace_driver(comp->dev.driver);
> +		if (!rtdrv->start)
> +			continue;
> +
> +		ret = rtdrv->start(comp);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(rvtrace_path_start);
> +
> +int rvtrace_path_stop(struct rvtrace_path *path)
> +{
> +	const struct rvtrace_driver *rtdrv;
> +	struct rvtrace_component *comp;
> +	struct rvtrace_path_node *node;
> +	int ret;
> +
> +	list_for_each_entry(node, &path->comp_list, head) {
> +		comp = node->comp;
> +		rtdrv = to_rvtrace_driver(comp->dev.driver);
> +		if (!rtdrv->stop)
> +			continue;
> +
> +		ret = rtdrv->stop(comp);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(rvtrace_path_stop);
> +
>   struct rvtrace_path *rvtrace_create_path(struct rvtrace_component *source,
>   					 struct rvtrace_component *sink,
>   					 enum rvtrace_component_mode mode)
> diff --git a/include/linux/rvtrace.h b/include/linux/rvtrace.h
> index f2174f463a69..e7bd335d388f 100644
> --- a/include/linux/rvtrace.h
> +++ b/include/linux/rvtrace.h
> @@ -273,10 +273,14 @@ struct rvtrace_path *rvtrace_create_path(struct rvtrace_component *source,
>   					 struct rvtrace_component *sink,
>   					 enum rvtrace_component_mode mode);
>   void rvtrace_destroy_path(struct rvtrace_path *path);
> +int rvtrace_path_start(struct rvtrace_path *path);
> +int rvtrace_path_stop(struct rvtrace_path *path);
>   
>   /**
>    * struct rvtrace_driver - Representation of a RISC-V trace driver
>    * id_table: Table to match components handled by the driver
> + * start:        Callback to start tracing
> + * stop:         Callback to stop tracing
>    * probe:        Driver probe() function
>    * remove:       Driver remove() function
>    * get_trace_id: Get/allocate a trace ID
> @@ -285,6 +289,8 @@ void rvtrace_destroy_path(struct rvtrace_path *path);
>    */
>   struct rvtrace_driver {
>   	const struct rvtrace_component_id *id_table;
> +	int			(*start)(struct rvtrace_component *comp);
> +	int			(*stop)(struct rvtrace_component *comp);
>   	int			(*probe)(struct rvtrace_component *comp);
>   	void			(*remove)(struct rvtrace_component *comp);
>   	int			(*get_trace_id)(struct rvtrace_component *comp,

I'd suggest add another function (*quiesce) or something like that. Trace
components have a tr??Empty bit that indicates trace has been all flushed
out. Also along the path when you do rvtrace_path_stop, you need to ensure
the source has stopped and quiescent before beginning to stop the sink.
Otherwise you'll get partial or corrupted trace. In essence, follow Control
Interface Spec 11.3 Enabling and Disabling. FYI: my userspace driver:
https://github.com/ganboing/riscv-trace-umd/blob/master/rvtrace/funnel.py#L223

Bo