Re: [PATCH v7 4/8] cxl: Add HDM-DB region creation

On Tue, Jul 28, 2026 at 07:41:32AM -0700, Davidlohr Bueso wrote:
> A region inherits its coherency from the chosen root decoder: HDM-DB
> if the root has CXL_DECODER_F_BI, otherwise HDM-H.
> 
> Surface the topology through read-only sysfs:
> 
>   - decoderX.Y/cap_bi (root): CFMWS BI restriction.
>   - decoderX.Y/bi (endpoint): '1' when configured for HDM-DB.

Hi Davidlohr,

$ grep What Documentation/ABI/testing/sysfs-bus-cxl
shows that we have a precedent for spelling things out in the
sysfs attribute names. Even long things like interleave_granularity
and extended_linear_cache_size. Suggest doing same for these.

one bit below..


> @@ -2108,10 +2106,31 @@ static int cxl_region_attach(struct cxl_region *cxlr,
>  		return -ENXIO;
>  	}
>  
> -	if (cxled->cxld.target_type != cxlr->type) {
> -		dev_dbg(&cxlr->dev, "%s:%s type mismatch: %d vs %d\n",
> -			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> -			cxled->cxld.target_type, cxlr->type);

The new checks below seem to ignore CXL_HDM_DECODER_COHERENCY_UNKNOWN.
Does the existing type check need to stay for UNKNOWNS?


> +	/*
> +	 * Verify the device and HDM are capable of the region's flavor before
> +	 * proceeding. The endpoint decoder's target_type is then inherited
> +	 * from cxlr->type later in cxl_rr_assign_decoder().
> +	 */
> +	if (cxlr->type == CXL_DECODER_DEVMEM &&
> +	    cxl_root_decoder_is_bi(cxlrd) && !cxlds->bi) {
> +		dev_err(&cxlr->dev, "%s:%s BI not enabled on device\n",
> +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev));
> +		return -ENXIO;
> +	}
> +
> +	cxlhdm = dev_get_drvdata(&ep_port->dev);
> +	if (!cxlhdm)
> +		return -ENXIO;
> +	if (cxlr->type == CXL_DECODER_HOSTONLYMEM &&
> +	    cxlhdm->supported_coherency == CXL_HDM_DECODER_COHERENCY_DEV) {
> +		dev_warn(&cxlr->dev, "%s:%s HDM is device-coherent only\n",
> +			 dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev));
> +		return -ENXIO;
> +	}
> +	if (cxlr->type == CXL_DECODER_DEVMEM &&
> +	    cxlhdm->supported_coherency == CXL_HDM_DECODER_COHERENCY_HOST) {
> +		dev_warn(&cxlr->dev, "%s:%s HDM is host-only coherent\n",
> +			 dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev));
>  		return -ENXIO;
>  	}

snip to end