Re: [PATCH v9 3/6] Coresight: Introduce a new struct coresight_path

[James Clark]

On 24/01/2025 7:25 am, Jie Gan wrote:
> Add 'struct coresight_path' to store the data that is needed by
> coresight_enable_path/coresight_disable_path. The structure
> will be transmitted to the helper and sink device to enable
> related funcationalities.
>
> Signed-off-by: Jie Gan <quic_jiegan@xxxxxxxxxxx>
> ---
>   drivers/hwtracing/coresight/coresight-core.c  | 87 ++++++++++++++-----
>   drivers/hwtracing/coresight/coresight-etb10.c |  3 +-
>   .../hwtracing/coresight/coresight-etm-perf.c  | 52 ++++++-----
>   .../hwtracing/coresight/coresight-etm-perf.h  |  2 +-
>   drivers/hwtracing/coresight/coresight-priv.h  | 21 +++--
>   drivers/hwtracing/coresight/coresight-sysfs.c | 32 +++----
>   .../hwtracing/coresight/coresight-tmc-etf.c   |  3 +-
>   .../hwtracing/coresight/coresight-tmc-etr.c   |  6 +-
>   drivers/hwtracing/coresight/coresight-trbe.c  |  4 +-
>   drivers/hwtracing/coresight/ultrasoc-smb.c    |  3 +-
>   10 files changed, 137 insertions(+), 76 deletions(-)

[...]


>   	INIT_LIST_HEAD(path);
> +	cs_path->path = path;
> +	/*
> +	 * Since not all source devices have a defined trace_id function,
> +	 * make sure to check for it before use.
> +	 *
> +	 * Assert the mode is CS_MODE_SYSFS, the trace_id will be assigned
> +	 * again later if the mode is CS_MODE_PERF.
> +	 */
> +	if (source_ops(source)->trace_id != NULL) {
> +		rc = source_ops(source)->trace_id(source, CS_MODE_SYSFS, NULL);

I don't think we should do this. Doesn't this consume two trace IDs for 
each session? And I'm not even sure if it's released properly if it's 
overwritten.

It should be possible to consolidate the all the trace ID allocation to 
a single step when building the path, or another function that gets 
called just after the path is built. At the moment the ID can be 
allocated from about 5 different places and it's quite hard to 
understand, especially with these new changes. I have some of it coded 
up, let me finish it off and I can share it.

> +		if(IS_VALID_CS_TRACE_ID(rc))
> +			cs_path->trace_id = rc;
> +		else
> +			cs_path->trace_id = 0;
> +	}
> +	else
> +		cs_path->trace_id = 0;

[...]

> +/**
> + * struct coresight_path - data needed by enable/disable path
> + * @handle:		perf aux handle for ETM.
> + * @path:		path from source to sink.
> + * @trace_id:		trace_id of the whole path.
> + */
> +struct coresight_path {
> +	struct perf_output_handle	*handle;

This is only needed to avoid adding *handle to the enable function call 
signature, but having it here implies it needs to be stored. And then we 
need to manage the lifecycle of it by nulling it on deletion. All of 
this can be avoided by just adding handle to enable().

Unrelated to this patch, but I'm not sure why we were passing around 
void* for handle either. It just makes the code hard to read and implies 
some flexibility that doesn't exist. It's always "struct 
perf_output_handle", so we can change void* to that in the enable 
functions. I also have a patch for this that I'll share in a bit.

> +	struct list_head		*path;
> +	u8				trace_id;
> +};
> +
>   static inline void coresight_insert_barrier_packet(void *buf)
>   {
>   	if (buf)
> @@ -132,16 +144,15 @@ static inline void CS_UNLOCK(void __iomem *addr)
>   	} while (0);
>   }
>   
> -void coresight_disable_path(struct list_head *path);
> -int coresight_enable_path(struct list_head *path, enum cs_mode mode,
> -			  void *sink_data);
> +void coresight_disable_path(struct coresight_path *cs_path);
> +int coresight_enable_path(struct coresight_path *cs_path, enum cs_mode mode);
>   struct coresight_device *coresight_get_sink(struct list_head *path);

This needs to be exported otherwise the build fails because you use it 
in a module in another commit. I assume you are building as static?