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

[Anup Patel]

On Wed, Oct 8, 2025 at 2:45 PM Bo Gan <ganboing at gmail.com> wrote:
>
> On 10/1/25 23:07, Anup Patel wrote:
> > From: Mayuresh Chitale <mchitale at ventanamicro.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 at ventanamicro.com>
> > Signed-off-by: Anup Patel <apatel at ventanamicro.com>
> > Signed-off-by: Mayuresh Chitale <mchitale at ventanamicro.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

It's better to add functions on a need basis rather than adding
it now without any potential user.

Regards,
Anu