cxl/hdm: Add support for 32 switch decoders

Per CXL r4.0 section 8.2.4.20.1. CXL host bridge and switch ports can
support 32 HDM decoders. Current implementation misses some decoders on
CXL host bridge and switch in the case that the value of Decoder Count
field in CXL HDM decoder Capability Register is greater than or equal to
9.

Update calculation implementation to ensure the decoder count calculation
is correct for CXL host bridge/switch ports.

Signed-off-by: Li Ming <ming.li@zohomail.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/20260321061459.1910205-1-ming.li@zohomail.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Author: liming011

drivers/cxl/core/hdm.c

@@ -177,7 +177,7 @@ static struct cxl_hdm *devm_cxl_setup_hdm(struct cxl_port *port,
 	}
 
 	parse_hdm_decoder_caps(cxlhdm);
-	if (cxlhdm->decoder_count == 0) {
+	if (cxlhdm->decoder_count < 0) {
 		dev_err(dev, "Spec violation. Caps invalid\n");
 		return ERR_PTR(-ENXIO);
 	}

drivers/cxl/cxl.h

@@ -77,7 +77,16 @@ static inline int cxl_hdm_decoder_count(u32 cap_hdr)
 {
 	int val = FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, cap_hdr);
 
-	return val ? val * 2 : 1;
+	switch (val) {
+	case 0:
+		return 1;
+	case 1 ... 8:
+		return val * 2;
+	case 9 ... 12:
+		return (val - 4) * 4;
+	default:
+		return -ENXIO;
+	}
 }
 
 /* Encode defined in CXL 2.0 8.2.5.12.7 HDM Decoder Control Register */

drivers/cxl/cxlmem.h

@@ -923,7 +923,7 @@ int cxl_mem_sanitize(struct cxl_memdev *cxlmd, u16 cmd);
  */
 struct cxl_hdm {
 	struct cxl_component_regs regs;
-	unsigned int decoder_count;
+	int decoder_count;
 	unsigned int target_count;
 	unsigned int interleave_mask;
 	unsigned long iw_cap_mask;