Re: [PATCH v2 1/2] interconnect: Add support for path tags

[Evan Green <evgreen@chromium.org>]

Hi Georgi and David,

On Tue, Jun 18, 2019 at 2:17 AM Georgi Djakov <georgi.djakov@linaro.org> wrote:
>
> Consumers may have use cases with different bandwidth requirements based
> on the system or driver state. The consumer driver can append a specific
> tag to the path and pass this information to the interconnect platform
> driver to do the aggregation based on this state.
>
> Introduce icc_set_tag() function that will allow the consumers to append
> an optional tag to each path. The aggregation of these tagged paths is
> platform specific.
>
> Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
> ---
>  drivers/interconnect/core.c           | 24 +++++++++++++++++++++++-
>  drivers/interconnect/qcom/sdm845.c    |  2 +-
>  include/linux/interconnect-provider.h |  4 ++--
>  include/linux/interconnect.h          |  5 +++++
>  4 files changed, 31 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> index 871eb4bc4efc..251354bb7fdc 100644
> --- a/drivers/interconnect/core.c
> +++ b/drivers/interconnect/core.c
> @@ -29,6 +29,7 @@ static struct dentry *icc_debugfs_dir;
>   * @req_node: entry in list of requests for the particular @node
>   * @node: the interconnect node to which this constraint applies
>   * @dev: reference to the device that sets the constraints
> + * @tag: path tag (optional)
>   * @avg_bw: an integer describing the average bandwidth in kBps
>   * @peak_bw: an integer describing the peak bandwidth in kBps
>   */
> @@ -36,6 +37,7 @@ struct icc_req {
>         struct hlist_node req_node;
>         struct icc_node *node;
>         struct device *dev;
> +       u32 tag;
>         u32 avg_bw;
>         u32 peak_bw;
>  };
> @@ -204,7 +206,7 @@ static int aggregate_requests(struct icc_node *node)
>         node->peak_bw = 0;
>
>         hlist_for_each_entry(r, &node->req_list, req_node)
> -               p->aggregate(node, r->avg_bw, r->peak_bw,
> +               p->aggregate(node, r->tag, r->avg_bw, r->peak_bw,
>                              &node->avg_bw, &node->peak_bw);
>
>         return 0;
> @@ -385,6 +387,26 @@ struct icc_path *of_icc_get(struct device *dev, const char *name)
>  }
>  EXPORT_SYMBOL_GPL(of_icc_get);
>
> +/**
> + * icc_set_tag() - set an optional tag on a path
> + * @path: the path we want to tag
> + * @tag: the tag value
> + *
> + * This function allows consumers to append a tag to the requests associated
> + * with a path, so that a different aggregation could be done based on this tag.
> + */
> +void icc_set_tag(struct icc_path *path, u32 tag)
> +{
> +       int i;
> +
> +       if (!path)
> +               return;
> +
> +       for (i = 0; i < path->num_nodes; i++)
> +               path->reqs[i].tag = tag;

It's a little unfortunate to have this tag sprayed across all the
request nodes in the path, even though it's really a single value. If
we thought there were likely to be more attributes common to a path
that a provider might want access to, we could add a pointer to the
path in icc_req, then stick the tag in the path. But if the tag ends
up being the only thing worth looking at, then I guess what you have
now is slightly better.