Subject: Re: [PATCH v2 1/9] Use IDR to maintain all the enabled sources' paths.

From: Mathieu Poirier <[email-masked]>
Date: Tue, 14 Dec 2021 11:30:10 -0700

Hi Mao,

On Thu, Dec 09, 2021 at 10:15:35PM +0800, Mao Jinlong wrote:
> Use hash length of the source's device name to map to the pointer
> of the enabled path. Using IDR will be more efficient than using
> the list. And there could be other sources except STM and CPU etms
> in the new HWs. It is better to maintain all the paths together.
> 
> Signed-off-by: Mao Jinlong <[email-masked]>
> ---
>  drivers/hwtracing/coresight/coresight-core.c | 76 +++++++-------------
>  1 file changed, 26 insertions(+), 50 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 8a18c71df37a..cc6b6cabf85f 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -7,6 +7,7 @@
>  #include <linux/init.h>
>  #include <linux/types.h>
>  #include <linux/device.h>
> +#include <linux/idr.h>
>  #include <linux/io.h>
>  #include <linux/err.h>
>  #include <linux/export.h>
> @@ -26,6 +27,12 @@
>  static DEFINE_MUTEX(coresight_mutex);
>  static DEFINE_PER_CPU(struct coresight_device *, csdev_sink);
>  
> +/*
> + * Use IDR to map the hash length of the source's device name
> + * to the pointer of path for the source
> + */
> +static DEFINE_IDR(path_idr);
> +
>  /**
>   * struct coresight_node - elements of a path, from source to sink
>   * @csdev:	Address of an element.
> @@ -36,20 +43,6 @@ struct coresight_node {
>  	struct list_head link;
>  };
>  
> -/*
> - * When operating Coresight drivers from the sysFS interface, only a single
> - * path can exist from a tracer (associated to a CPU) to a sink.
> - */
> -static DEFINE_PER_CPU(struct list_head *, tracer_path);
> -
> -/*
> - * As of this writing only a single STM can be found in CS topologies.  Since
> - * there is no way to know if we'll ever see more and what kind of
> - * configuration they will enact, for the time being only define a single path
> - * for STM.
> - */
> -static struct list_head *stm_path;
> -
>  /*
>   * When losing synchronisation a new barrier packet needs to be inserted at the
>   * beginning of the data collected in a buffer.  That way the decoder knows that
> @@ -1088,10 +1081,11 @@ static int coresight_validate_source(struct coresight_device *csdev,
>  
>  int coresight_enable(struct coresight_device *csdev)
>  {
> -	int cpu, ret = 0;
> +	int ret = 0;
>  	struct coresight_device *sink;
>  	struct list_head *path;
>  	enum coresight_dev_subtype_source subtype;
> +	u32 hash;
>  
>  	subtype = csdev->subtype.source_subtype;
>  
> @@ -1133,26 +1127,14 @@ int coresight_enable(struct coresight_device *csdev)
>  	if (ret)
>  		goto err_source;
>  
> -	switch (subtype) {
> -	case CORESIGHT_DEV_SUBTYPE_SOURCE_PROC:
> -		/*
> -		 * When working from sysFS it is important to keep track
> -		 * of the paths that were created so that they can be
> -		 * undone in 'coresight_disable()'.  Since there can only
> -		 * be a single session per tracer (when working from sysFS)
> -		 * a per-cpu variable will do just fine.
> -		 */
> -		cpu = source_ops(csdev)->cpu_id(csdev);
> -		per_cpu(tracer_path, cpu) = path;
> -		break;
> -	case CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE:
> -		stm_path = path;
> -		break;
> -	default:
> -		/* We can't be here */
> -		break;
> -	}
> -
> +	/*
> +	 * Use the hash length of source's device name as ID
> +	 * and map the ID to the pointer of the path.
> +	 */
> +	hash = hashlen_hash(hashlen_string(NULL, dev_name(&csdev->dev)));
> +	ret = idr_alloc_u32(&path_idr, path, &hash, hash, GFP_KERNEL);
> +	if (ret)
> +		goto err_source;
>  out:
>  	mutex_unlock(&coresight_mutex);
>  	return ret;
> @@ -1168,8 +1150,9 @@ EXPORT_SYMBOL_GPL(coresight_enable);
>  
>  void coresight_disable(struct coresight_device *csdev)
>  {
> -	int cpu, ret;
> +	int ret;
>  	struct list_head *path = NULL;
> +	u32 hash;
>  
>  	mutex_lock(&coresight_mutex);
>  
> @@ -1180,21 +1163,13 @@ void coresight_disable(struct coresight_device *csdev)
>  	if (!csdev->enable || !coresight_disable_source(csdev))
>  		goto out;
>  
> -	switch (csdev->subtype.source_subtype) {
> -	case CORESIGHT_DEV_SUBTYPE_SOURCE_PROC:
> -		cpu = source_ops(csdev)->cpu_id(csdev);
> -		path = per_cpu(tracer_path, cpu);
> -		per_cpu(tracer_path, cpu) = NULL;
> -		break;
> -	case CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE:
> -		path = stm_path;
> -		stm_path = NULL;
> -		break;
> -	default:
> -		/* We can't be here */
> -		break;
> -	}
> +	hash = hashlen_hash(hashlen_string(NULL, dev_name(&csdev->dev)));
> +	/* Find the path by the hash length. */
> +	path = idr_find(&path_idr, hash);
> +	if (path == NULL)
> +		return;

Please add a dev_err() here as this should really not be happening.

>  
> +	idr_remove(&path_idr, hash);
>  	coresight_disable_path(path);
>  	coresight_release_path(path);
>  
> @@ -1779,6 +1754,7 @@ static int __init coresight_init(void)
>  
>  static void __exit coresight_exit(void)
>  {
> +	idr_destroy(&path_idr);

As far as I can tell this isn't needed.

>  	cscfg_exit();
>  	etm_perf_exit();
>  	bus_unregister(&coresight_bustype);
> -- 
> 2.17.1
> 

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