Re: [PATCH 4/5] cxl/port: Scan single-target ports for decoders

[Alison Schofield <alison.schofield@intel.com>]

On Fri, Apr 14, 2023 at 11:54:11AM -0700, Dan Williams wrote:
> Do not assume that a single-target port falls back to a passthrough
> decoder configuration. Scan for decoders and only fallback after probing
> that the HDM decoder capability is not present.
> 
> One user visible affect of this bug is the inability to enumerate
> present CXL regions as the decoder settings for the present decoders are
> skipped.
> 
> Fixes: d17d0540a0db ("cxl/core/hdm: Add CXL standard decoder enumeration to the core")
> Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Link: http://lore.kernel.org/r/20230227153128.8164-1-Jonathan.Cameron@huawei.com
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Alison Schofield <alison.schofield@intel.com>

> ---
>  drivers/cxl/core/hdm.c |    5 +++--
>  drivers/cxl/port.c     |   18 +++++++++++++-----
>  2 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 6fdf7981ddc7..abe3877cfa63 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -92,8 +92,9 @@ static int map_hdm_decoder_regs(struct cxl_port *port, void __iomem *crb,
>  
>  	cxl_probe_component_regs(&port->dev, crb, &map.component_map);
>  	if (!map.component_map.hdm_decoder.valid) {
> -		dev_err(&port->dev, "HDM decoder registers invalid\n");
> -		return -ENXIO;
> +		dev_dbg(&port->dev, "HDM decoder registers not implemented\n");
> +		/* unique error code to indicate no HDM decoder capability */
> +		return -ENODEV;
>  	}
>  
>  	return cxl_map_component_regs(&port->dev, regs, &map,
> diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
> index 22a7ab2bae7c..eb57324c4ad4 100644
> --- a/drivers/cxl/port.c
> +++ b/drivers/cxl/port.c
> @@ -66,14 +66,22 @@ static int cxl_switch_port_probe(struct cxl_port *port)
>  	if (rc < 0)
>  		return rc;
>  
> -	if (rc == 1)
> -		return devm_cxl_add_passthrough_decoder(port);
> -
>  	cxlhdm = devm_cxl_setup_hdm(port, NULL);
> -	if (IS_ERR(cxlhdm))
> +	if (!IS_ERR(cxlhdm))
> +		return devm_cxl_enumerate_decoders(cxlhdm, NULL);
> +
> +	if (PTR_ERR(cxlhdm) != -ENODEV) {
> +		dev_err(&port->dev, "Failed to map HDM decoder capability\n");
>  		return PTR_ERR(cxlhdm);
> +	}
> +
> +	if (rc == 1) {
> +		dev_dbg(&port->dev, "Fallback to passthrough decoder\n");
> +		return devm_cxl_add_passthrough_decoder(port);
> +	}
>  
> -	return devm_cxl_enumerate_decoders(cxlhdm, NULL);
> +	dev_err(&port->dev, "HDM decoder capability not found\n");
> +	return -ENXIO;
>  }
>  
>  static int cxl_endpoint_port_probe(struct cxl_port *port)
>