Re: [PATCH v4 01/14] cxl/region: Store root decoder in struct cxl_region

Jonathan Cameron
2025-11-11T14:45:45Z

On Mon, 3 Nov 2025 19:47:42 +0100
Robert Richter <rrichter@amd.com> wrote:

> A region is always bound to a root decoder. The region's associated
> root decoder is often needed. Add it to struct cxl_region.
>
> This simplifies the code by removing dynamic lookups and the root
> decoder argument from the function argument list where possible.
>
> Patch is a prerequisite to implement address translation which uses
> struct cxl_region to store all relevant region and interleaving
> parameters. It changes the argument list of __construct_region() in
> preparation of adding a context argument. Additionally the arg list of
> cxl_region_attach_position() is simplified and the use of
> to_cxl_root_decoder() removed, which always reconstructs and checks
> the pointer. The pointer never changes and is frequently used. Code
> becomes more readable as this amphazises the binding between both
> objects.
>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Reviewed-by: Gregory Price <gourry@gourry.net>
> Signed-off-by: Robert Richter <rrichter@amd.com>

Just a note to say this will (maybe just context) clash with Alejandro's rework
around construct_region_begin()

https://lore.kernel.org/all/20251110153657.2706192-19-alejandro.lucero-palau@amd.com/

Probably easy to resolve, but worth both of you being aware if you hadn't noticed
already!

Jonathan

> ---
> drivers/cxl/core/region.c | 37 +++++++++++++++++++------------------
> drivers/cxl/cxl.h | 2 ++
> 2 files changed, 21 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index b06fee1978ba..45b1386a18d7 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -495,9 +495,9 @@ static ssize_t interleave_ways_store(struct device *dev,
> struct device_attribute *attr,
> const char *buf, size_t len)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
> - struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
> struct cxl_region *cxlr = to_cxl_region(dev);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> + struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
> struct cxl_region_params *p = &cxlr->params;
> unsigned int val, save;
> int rc;
> @@ -558,9 +558,9 @@ static ssize_t interleave_granularity_store(struct device *dev,
> struct device_attribute *attr,
> const char *buf, size_t len)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
> - struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
> struct cxl_region *cxlr = to_cxl_region(dev);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> + struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
> struct cxl_region_params *p = &cxlr->params;
> int rc, val;
> u16 ig;
> @@ -634,7 +634,7 @@ static DEVICE_ATTR_RO(mode);
>
> static int alloc_hpa(struct cxl_region *cxlr, resource_size_t size)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> struct cxl_region_params *p = &cxlr->params;
> struct resource *res;
> u64 remainder = 0;
> @@ -1327,7 +1327,7 @@ static int cxl_port_setup_targets(struct cxl_port *port,
> struct cxl_region *cxlr,
> struct cxl_endpoint_decoder *cxled)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> int parent_iw, parent_ig, ig, iw, rc, inc = 0, pos = cxled->pos;
> struct cxl_port *parent_port = to_cxl_port(port->dev.parent);
> struct cxl_region_ref *cxl_rr = cxl_rr_load(port, cxlr);
> @@ -1686,10 +1686,10 @@ static int cxl_region_validate_position(struct cxl_region *cxlr,
> }
>
> static int cxl_region_attach_position(struct cxl_region *cxlr,
> - struct cxl_root_decoder *cxlrd,
> struct cxl_endpoint_decoder *cxled,
> const struct cxl_dport *dport, int pos)
> {
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> struct cxl_switch_decoder *cxlsd = &cxlrd->cxlsd;
> struct cxl_decoder *cxld = &cxlsd->cxld;
> @@ -1926,7 +1926,7 @@ static int cxl_region_sort_targets(struct cxl_region *cxlr)
> static int cxl_region_attach(struct cxl_region *cxlr,
> struct cxl_endpoint_decoder *cxled, int pos)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> struct cxl_dev_state *cxlds = cxlmd->cxlds;
> struct cxl_region_params *p = &cxlr->params;
> @@ -2031,8 +2031,7 @@ static int cxl_region_attach(struct cxl_region *cxlr,
> ep_port = cxled_to_port(cxled);
> dport = cxl_find_dport_by_dev(root_port,
> ep_port->host_bridge);
> - rc = cxl_region_attach_position(cxlr, cxlrd, cxled,
> - dport, i);
> + rc = cxl_region_attach_position(cxlr, cxled, dport, i);
> if (rc)
> return rc;
> }
> @@ -2055,7 +2054,7 @@ static int cxl_region_attach(struct cxl_region *cxlr,
> if (rc)
> return rc;
>
> - rc = cxl_region_attach_position(cxlr, cxlrd, cxled, dport, pos);
> + rc = cxl_region_attach_position(cxlr, cxled, dport, pos);
> if (rc)
> return rc;
>
> @@ -2351,8 +2350,8 @@ static const struct attribute_group *region_groups[] = {
>
> static void cxl_region_release(struct device *dev)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
> struct cxl_region *cxlr = to_cxl_region(dev);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> int id = atomic_read(&cxlrd->region_id);
>
> /*
> @@ -2435,10 +2434,12 @@ static struct cxl_region *cxl_region_alloc(struct cxl_root_decoder *cxlrd, int i
> * region id allocations
> */
> get_device(dev->parent);
> + cxlr->cxlrd = cxlrd;
> + cxlr->id = id;
> +
> device_set_pm_not_required(dev);
> dev->bus = &cxl_bus_type;
> dev->type = &cxl_region_type;
> - cxlr->id = id;
>
> return cxlr;
> }
> @@ -2937,7 +2938,7 @@ static bool has_spa_to_hpa(struct cxl_root_decoder *cxlrd)
> u64 cxl_dpa_to_hpa(struct cxl_region *cxlr, const struct cxl_memdev *cxlmd,
> u64 dpa)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> u64 dpa_offset, hpa_offset, bits_upper, mask_upper, hpa;
> struct cxl_region_params *p = &cxlr->params;
> struct cxl_endpoint_decoder *cxled = NULL;
> @@ -3013,7 +3014,7 @@ static int region_offset_to_dpa_result(struct cxl_region *cxlr, u64 offset,
> struct dpa_result *result)
> {
> struct cxl_region_params *p = &cxlr->params;
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> struct cxl_endpoint_decoder *cxled;
> u64 hpa, hpa_offset, dpa_offset;
> u64 bits_upper, bits_lower;
> @@ -3404,7 +3405,7 @@ static int match_region_by_range(struct device *dev, const void *data)
> static int cxl_extended_linear_cache_resize(struct cxl_region *cxlr,
> struct resource *res)
> {
> - struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> struct cxl_region_params *p = &cxlr->params;
> resource_size_t size = resource_size(res);
> resource_size_t cache_size, start;
> @@ -3440,9 +3441,9 @@ static int cxl_extended_linear_cache_resize(struct cxl_region *cxlr,
> }
>
> static int __construct_region(struct cxl_region *cxlr,
> - struct cxl_root_decoder *cxlrd,
> struct cxl_endpoint_decoder *cxled)
> {
> + struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> struct range *hpa = &cxled->cxld.hpa_range;
> struct cxl_region_params *p;
> @@ -3534,7 +3535,7 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
> return cxlr;
> }
>
> - rc = __construct_region(cxlr, cxlrd, cxled);
> + rc = __construct_region(cxlr, cxled);
> if (rc) {
> devm_release_action(port->uport_dev, unregister_region, cxlr);
> return ERR_PTR(rc);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 231ddccf8977..19b8b62a1322 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -521,6 +521,7 @@ enum cxl_partition_mode {
> * struct cxl_region - CXL region
> * @dev: This region's device
> * @id: This region's id. Id is globally unique across all regions
> + * @cxlrd: Region's root decoder
> * @mode: Operational mode of the mapped capacity
> * @type: Endpoint decoder target type
> * @cxl_nvb: nvdimm bridge for coordinating @cxlr_pmem setup / shutdown
> @@ -534,6 +535,7 @@ enum cxl_partition_mode {
> struct cxl_region {
> struct device dev;
> int id;
> + struct cxl_root_decoder *cxlrd;
> enum cxl_partition_mode mode;
> enum cxl_decoder_type type;
> struct cxl_nvdimm_bridge *cxl_nvb;