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

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 2 Sep 2021 12:50:08 -0700
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>

Comments inline...

> ---
>  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)

Why do we let nr_targets go negative?  Could make the parameter unsigned perhaps or
check for that here (even though it makes no sense).

> +	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;

Hmm. Whilst the check seems valid, it's a bit inelegant.
The capability register unhelpfully simply has it defined
as not applicable rather than 0, so I'd be nervous that might
end up here (not checked yet).

>  	/* 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;
> @@ -532,9 +552,11 @@ int cxl_decoder_add(struct device *host, struct cxl_decoder *cxld,
>  	if (IS_ERR(cxld))
>  		return PTR_ERR(cxld);
>  
> +	dev = &cxld->dev;
> +
>  	port = to_cxl_port(cxld->dev.parent);
>  	device_lock(&port->dev);
> -	if (list_empty(&port->dports)) {
> +	if (is_endpoint_decoder(dev) && list_empty(&port->dports)) {
>  		rc = -EINVAL;
>  		goto out_unlock;
>  	}
> @@ -551,7 +573,6 @@ int cxl_decoder_add(struct device *host, struct cxl_decoder *cxld,
>  	}
>  	device_unlock(&port->dev);
>  
> -	dev = &cxld->dev;
>  	rc = dev_set_name(dev, "decoder%d.%d", port->id, cxld->id);
>  	if (rc)
>  		return rc;