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

From: Ben Widawsky <ben.widawsky@intel.com>
To: Dan Williams <dan.j.williams@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: Mon, 13 Sep 2021 09:11:49 -0700	[thread overview]
Message-ID: <20210913161149.ggbd5jmro2davaq5@intel.com> (raw)
In-Reply-To: <CAPcyv4gbVtZywtzYVFS_KAQ_aHGHDQtke=eeVSv3pdz=CfVOhA@mail.gmail.com>

On 21-09-10 12:19:24, Dan Williams wrote:
> 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.

I didn't see a need as of yet to differentiate between endpoint ports and other
ports. I don't entirely understand what you mean by "allowing a switch port to
carry an endpoint decoder" means. Can you please elaborate?