Re: [PATCH 12/23] cxl: Introduce endpoint decoders

[Ben Widawsky <ben.widawsky@intel.com>]

On 21-11-22 16:20:39, Jonathan Cameron wrote:
> On Fri, 19 Nov 2021 16:02:39 -0800
> 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>
> 
> I'm not a fan of special values like using 0 here to indicate endpoint
> device.  I'd rather see a base cxl_decode_alloc(..., bool ep)
> and possibly wrappers for the non ep case and ep one.
> 
> Jonathan
> 

My inclination is the opposite. However, I think you and Dan both brought up
something to this effect in the previous RFCs.

Dan, do you have a preference here?

> > ---
> >  drivers/cxl/core/bus.c | 41 +++++++++++++++++++++++++++++++++--------
> >  1 file changed, 33 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/cxl/core/bus.c b/drivers/cxl/core/bus.c
> > index 1ee12a60f3f4..16b15f54fb62 100644
> > --- a/drivers/cxl/core/bus.c
> > +++ b/drivers/cxl/core/bus.c
> > @@ -187,6 +187,12 @@ 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);
> > @@ -196,6 +202,12 @@ 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,
> > @@ -208,6 +220,11 @@ 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;
> > @@ -499,7 +516,9 @@ static int decoder_populate_targets(struct cxl_decoder *cxld,
> >   * cxl_decoder_alloc - Allocate a new CXL decoder
> >   * @port: owning port of this decoder
> >   * @nr_targets: downstream targets accessible by this decoder. All upstream
> > - *		ports and root ports must have at least 1 target.
> > + *		ports and root ports must have at least 1 target. Endpoint
> > + *		devices will have 0 targets. Callers wishing to register an
> > + *		endpoint device should specify 0.
> >   *
> >   * A port should contain one or more decoders. Each of those decoders enable
> >   * some address space for CXL.mem utilization. A decoder is expected to be
> > @@ -516,7 +535,7 @@ struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port,
> >  	struct device *dev;
> >  	int rc = 0;
> >  
> > -	if (nr_targets > CXL_DECODER_MAX_INTERLEAVE || nr_targets == 0)
> > +	if (nr_targets > CXL_DECODER_MAX_INTERLEAVE)
> >  		return ERR_PTR(-EINVAL);
> >  
> >  	cxld = kzalloc(struct_size(cxld, target, nr_targets), GFP_KERNEL);
> > @@ -535,8 +554,11 @@ struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port,
> >  	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;
> >  	/* root ports do not have a cxl_port_type parent */
> > -	if (port->dev.parent->type == &cxl_port_type)
> > +	else if (port->dev.parent->type == &cxl_port_type)
> >  		dev->type = &cxl_decoder_switch_type;
> >  	else
> >  		dev->type = &cxl_decoder_root_type;
> > @@ -579,12 +601,15 @@ int cxl_decoder_add(struct cxl_decoder *cxld, int *target_map)
> >  	if (cxld->interleave_ways < 1)
> >  		return -EINVAL;
> >  
> > -	port = to_cxl_port(cxld->dev.parent);
> > -	rc = decoder_populate_targets(cxld, port, target_map);
> > -	if (rc)
> > -		return rc;
> > -
> >  	dev = &cxld->dev;
> > +
> > +	port = to_cxl_port(cxld->dev.parent);
> > +	if (!is_endpoint_decoder(dev)) {
> > +		rc = decoder_populate_targets(cxld, port, target_map);
> > +		if (rc)
> > +			return rc;
> > +	}
> > +
> >  	rc = dev_set_name(dev, "decoder%d.%d", port->id, cxld->id);
> >  	if (rc)
> >  		return rc;
>