Re: [PATCH v25 06/11] cxl/hdm: Add support for getting region from committed decoder

[Dan Williams <dan.j.williams@intel.com>]

alejandro.lucero-palau@ wrote:
> From: Alejandro Lucero <alucerop@amd.com>
> 
> A Type2 device configured by the BIOS can have its HDM committed and
> a cxl region linked by auto discovery when the device memdev is created.
> 
> Add a function for a Type2 driver to obtain such a region.
> 
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
[..]
> +/**
> + * cxl_get_region_from_committed_decoder - obtain a pointer to a region
> + * @cxlmd: CXL memdev from an endpoint device
> + *
> + * An accelerator decoder can be set up by the firmware/BIOS and the auto
> + * discovery region creation triggered by the memdev object initialization.
> + * Using this function the related driver can obtain such a region.
> + *
> + * Only one committed HDM is expected, returning the first one found.
> + *
> + * Return pointer to a region or NULL
> + */
> +struct cxl_region *cxl_get_region_from_committed_decoder(struct cxl_memdev *cxlmd)
> +{
> +	struct cxl_port *endpoint = cxlmd->endpoint;
> +	struct cxl_endpoint_decoder *cxled;
> +
> +	if (!endpoint)
> +		return NULL;
> +
> +	guard(rwsem_read)(&cxl_rwsem.dpa);
> +	struct device *cxled_dev __free(put_device) =
> +		device_find_child(&endpoint->dev, NULL,
> +				  find_committed_endpoint_decoder);
> +
> +	if (!cxled_dev)
> +		return NULL;
> +
> +	cxled = to_cxl_endpoint_decoder(cxled_dev);
> +
> +	return cxled->cxld.region;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_get_region_from_committed_decoder, "CXL");

As soon as this function returns there is no guarantee that the region
is still valid.