Re: [PATCH v1 2/3] coresight: Add reserve trace id support

[James Clark <james.clark@arm.com>]

On 16/05/2024 04:56, Mao Jinlong wrote:
> Dynamic trace id was introduced in coresight subsystem so trace id is
> allocated dynamically. However, some hardware ATB source has static trace
> id and it cannot be changed via software programming. Reserve trace id
> for this kind of hardware source.
> 
> Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
> ---
>  .../hwtracing/coresight/coresight-platform.c  | 26 +++++++++++++++++++
>  .../hwtracing/coresight/coresight-trace-id.c  | 24 +++++++++++++++++
>  .../hwtracing/coresight/coresight-trace-id.h  | 11 ++++++++
>  include/linux/coresight.h                     |  1 +
>  4 files changed, 62 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-platform.c b/drivers/hwtracing/coresight/coresight-platform.c
> index 9d550f5697fa..d3e22a2608df 100644
> --- a/drivers/hwtracing/coresight/coresight-platform.c
> +++ b/drivers/hwtracing/coresight/coresight-platform.c
> @@ -183,6 +183,17 @@ static int of_coresight_get_cpu(struct device *dev)
>  	return cpu;
>  }
>  
> +/*
> + * of_coresight_get_trace_id: Get the atid of a source device.
> + *
> + * Returns 0 on success.
> + */
> +static int of_coresight_get_trace_id(struct device *dev, u32 *id)
> +{
> +
> +	return of_property_read_u32(dev->of_node, "trace-id", id);
> +}
> +
>  /*
>   * of_coresight_parse_endpoint : Parse the given output endpoint @ep
>   * and fill the connection information in @pdata->out_conns
> @@ -315,6 +326,12 @@ static inline int of_coresight_get_cpu(struct device *dev)
>  {
>  	return -ENODEV;
>  }
> +
> +static int of_coresight_get_trace_id(struct device *dev, u32 *id)
> +{
> +	return -ENODEV;
> +}
> +
>  #endif
>  
>  #ifdef CONFIG_ACPI
> @@ -794,6 +811,15 @@ int coresight_get_cpu(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(coresight_get_cpu);
>  
> +int coresight_get_trace_id(struct device *dev, u32 *id)
> +{
> +	if (!is_of_node(dev->fwnode))
> +		return -EINVAL;
> +
> +	return of_coresight_get_trace_id(dev, id);
> +}
> +EXPORT_SYMBOL_GPL(coresight_get_trace_id);
> +
>  struct coresight_platform_data *
>  coresight_get_platform_data(struct device *dev)
>  {
> diff --git a/drivers/hwtracing/coresight/coresight-trace-id.c b/drivers/hwtracing/coresight/coresight-trace-id.c
> index af5b4ef59cea..536a34e9de6f 100644
> --- a/drivers/hwtracing/coresight/coresight-trace-id.c
> +++ b/drivers/hwtracing/coresight/coresight-trace-id.c
> @@ -110,6 +110,24 @@ static int coresight_trace_id_alloc_new_id(struct coresight_trace_id_map *id_map
>  	return id;
>  }
>  
> +static int coresight_trace_id_set(int id, struct coresight_trace_id_map *id_map)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&id_map_lock, flags);
> +
> +	if (WARN(!IS_VALID_CS_TRACE_ID(id), "Invalid Trace ID %d\n", id))
> +		return -EINVAL;
> +	if (WARN(test_bit(id, id_map->used_ids), "ID is already used: %d\n", id))
> +		return -EINVAL;

Do these returns not skip unlocking the spinlock?

It might be slightly fewer changes if we update the existing
coresight_trace_id_alloc_new_id() to add a new "only_preferred" option.

Then use the existing system id allocator which already handles the lock
and unlock properly:

  static int coresight_trace_id_map_get_system_id(struct
                             coresight_trace_id_map *id_map, int id,

                             bool only_preferred)
  {
  ...
	spin_lock_irqsave(&id_map_lock, flags);
	/* prefer odd IDs for system components to avoid legacy CPU IDS
	id = coresight_trace_id_alloc_new_id(id_map, id, true,
                                             only_preferred);
        spin_unlock_irqrestore(&id_map_lock, flags);
  ...

I suppose the end result is the same as your implementation, but it
trades making one existing function slightly more complicated instead of
adding some new ones.