Re: [PATCH v4 07/14] cxl/region: Use region data to get the root decoder

Dave Jiang
2025-11-03T22:30:13Z

On 11/3/25 11:47 AM, Robert Richter wrote:
> To find a region's root decoder, the endpoint's HPA range is used to
> search the matching decoder by its range. With address translation the
> endpoint decoder's range is in a different address space and thus
> cannot be used to determine the root decoder.
>
> The region parameters are encapsulated within struc cxl_region_context
> and may include the translated Host Physical Address (HPA) range. Use
> this context to identify the root decoder rather than relying on the
> endpoint.
>
> Modify cxl_find_root_decoder() and add the region context as
> parameter. Rename this function to get_cxl_root_decoder() as a
> counterpart to put_cxl_root_decoder(). Simplify the implementation by
> removing function cxl_port_find_switch_decode(). The function is
> unnecessary because it is not referenced or utilized elsewhere in the
> code.
>
> Signed-off-by: Robert Richter <rrichter@amd.com>

Just a nit below. Otherwise
Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
> drivers/cxl/core/region.c | 50 +++++++++++++++++----------------------
> 1 file changed, 22 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 2cfc29a2b588..2dd9e9be4889 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3350,47 +3350,39 @@ static int devm_cxl_add_dax_region(struct cxl_region *cxlr)
> return rc;
> }
>
> -static int match_decoder_by_range(struct device *dev, const void *data)
> +static int match_root_decoder(struct device *dev, const void *data)
> {
> const struct range *r1, *r2 = data;
> - struct cxl_decoder *cxld;
> + struct cxl_root_decoder *cxlrd;
>
> - if (!is_switch_decoder(dev))
> + if (!is_root_decoder(dev))
> return 0;
>
> - cxld = to_cxl_decoder(dev);
> - r1 = &cxld->hpa_range;
> - return range_contains(r1, r2);
> -}
> + cxlrd = to_cxl_root_decoder(dev);
> + r1 = &cxlrd->cxlsd.cxld.hpa_range;
>
> -static struct cxl_decoder *
> -cxl_port_find_switch_decoder(struct cxl_port *port, struct range *hpa_range)
> -{
> - struct device *cxld_dev = device_find_child(&port->dev, hpa_range,
> - match_decoder_by_range);
> -
> - return cxld_dev ? to_cxl_decoder(cxld_dev) : NULL;
> + return range_contains(r1, r2);
> }
>
> static struct cxl_root_decoder *
> -cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
> +get_cxl_root_decoder(struct cxl_endpoint_decoder *cxled,
> + struct cxl_region_context *ctx)

Would like a comment that make note the caller should call put_device() when done with the root decoder.

DJ
> {
> - struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> struct cxl_port *port = cxled_to_port(cxled);
> struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
> - struct cxl_decoder *root, *cxld = &cxled->cxld;
> - struct range *hpa_range = &cxld->hpa_range;
> + struct device *cxlrd_dev;
>
> - root = cxl_port_find_switch_decoder(&cxl_root->port, hpa_range);
> - if (!root) {
> - dev_err(cxlmd->dev.parent,
> + cxlrd_dev = device_find_child(&cxl_root->port.dev, &ctx->hpa_range,
> + match_root_decoder);
> + if (!cxlrd_dev) {
> + dev_err(port->uport_dev,
> "%s:%s no CXL window for range %#llx:%#llx\n",
> - dev_name(&cxlmd->dev), dev_name(&cxld->dev),
> - hpa_range->start, hpa_range->end);
> - return NULL;
> + dev_name(&ctx->cxlmd->dev), dev_name(&cxled->cxld.dev),
> + ctx->hpa_range.start, ctx->hpa_range.end);
> + return ERR_PTR(-ENXIO);
> }
>
> - return to_cxl_root_decoder(&root->dev);
> + return to_cxl_root_decoder(cxlrd_dev);
> }
>
> static int match_region_by_range(struct device *dev, const void *data)
> @@ -3584,9 +3576,11 @@ int cxl_add_to_region(struct cxl_endpoint_decoder *cxled)
> };
>
> struct cxl_root_decoder *cxlrd __free(put_cxl_root_decoder) =
> - cxl_find_root_decoder(cxled);
> - if (!cxlrd)
> - return -ENXIO;
> + get_cxl_root_decoder(cxled, &ctx);
> +
> + rc = PTR_ERR_OR_ZERO(cxlrd);
> + if (rc)
> + return rc;
>
> /*
> * Ensure that if multiple threads race to construct_region()