Re: [PATCH 04/13] cxl: Introduce endpoint decoders

From: Dan Williams <dan.j.williams@intel.com>
To: Ben Widawsky <ben.widawsky@intel.com>
Cc: linux-cxl@vger.kernel.org,
	Alison Schofield <alison.schofield@intel.com>,
	Ira Weiny <ira.weiny@intel.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Vishal Verma <vishal.l.verma@intel.com>
Subject: Re: [PATCH 04/13] cxl: Introduce endpoint decoders
Date: Fri, 10 Sep 2021 12:19:24 -0700	[thread overview]
Message-ID: <CAPcyv4gbVtZywtzYVFS_KAQ_aHGHDQtke=eeVSv3pdz=CfVOhA@mail.gmail.com> (raw)
In-Reply-To: <20210902195017.2516472-5-ben.widawsky@intel.com>

On Thu, Sep 2, 2021 at 12:50 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> Endpoints have decoders too. It is useful to share the same
> infrastructure from cxl_core. Endpoints do not have dports (downstream
> targets), only the underlying physical medium. As a result, some special
> casing is needed.
>
> There is no functional change introduced yet as endpoints don't actually
> enumerate decoders yet.
>
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> ---
>  drivers/cxl/core/bus.c | 29 +++++++++++++++++++++++++----
>  1 file changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/cxl/core/bus.c b/drivers/cxl/core/bus.c
> index 8d5061b0794d..6202ce5a5ac2 100644
> --- a/drivers/cxl/core/bus.c
> +++ b/drivers/cxl/core/bus.c
> @@ -175,6 +175,12 @@ static const struct attribute_group *cxl_decoder_switch_attribute_groups[] = {
>         NULL,
>  };
>
> +static const struct attribute_group *cxl_decoder_endpoint_attribute_groups[] = {
> +       &cxl_decoder_base_attribute_group,
> +       &cxl_base_attribute_group,
> +       NULL,
> +};
> +
>  static void cxl_decoder_release(struct device *dev)
>  {
>         struct cxl_decoder *cxld = to_cxl_decoder(dev);
> @@ -184,6 +190,12 @@ static void cxl_decoder_release(struct device *dev)
>         kfree(cxld);
>  }
>
> +static const struct device_type cxl_decoder_endpoint_type = {
> +       .name = "cxl_decoder_endpoint",
> +       .release = cxl_decoder_release,
> +       .groups = cxl_decoder_endpoint_attribute_groups,
> +};
> +
>  static const struct device_type cxl_decoder_switch_type = {
>         .name = "cxl_decoder_switch",
>         .release = cxl_decoder_release,
> @@ -196,6 +208,11 @@ static const struct device_type cxl_decoder_root_type = {
>         .groups = cxl_decoder_root_attribute_groups,
>  };
>
> +static bool is_endpoint_decoder(struct device *dev)
> +{
> +       return dev->type == &cxl_decoder_endpoint_type;
> +}
> +
>  bool is_root_decoder(struct device *dev)
>  {
>         return dev->type == &cxl_decoder_root_type;
> @@ -472,7 +489,7 @@ struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, int nr_targets)
>         struct device *dev;
>         int rc = 0;
>
> -       if (nr_targets > CXL_DECODER_MAX_INTERLEAVE || nr_targets < 1)
> +       if (nr_targets > CXL_DECODER_MAX_INTERLEAVE)
>                 return ERR_PTR(-EINVAL);
>
>         cxld = kzalloc(struct_size(cxld, target, nr_targets), GFP_KERNEL);
> @@ -491,8 +508,11 @@ struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, int nr_targets)
>         dev->parent = &port->dev;
>         dev->bus = &cxl_bus_type;
>
> +       /* Endpoints don't have a target list */
> +       if (nr_targets == 0)
> +               dev->type = &cxl_decoder_endpoint_type;

Do you also plan to introduce the concept of endpoint ports, and if
yes should that come before this patch? That would seem to be more
robust than, for example, allowing a switch port to carry an endpoint
decoder object as this allows.