[PATCH] cxl/hdm: Add support for 32 switch decoders

Li Ming
2026-03-18T13:01:56Z

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>
---
drivers/cxl/cxl.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 9b947286eb9b..466b8eeefed7 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -77,7 +77,12 @@ 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;
+ if (!val)
+ return 1;
+ else if (val <= 8)
+ return val * 2;
+ else
+ return 4 * (val - 4);
}

/* Encode defined in CXL 2.0 8.2.5.12.7 HDM Decoder Control Register */

---
base-commit: f338e77383789c0cae23ca3d48adcc5e9e137e3c
change-id: 20260318-add_support_for_32_decoders-4a7c77949a41

Best regards,
--
Li Ming <ming.li@zohomail.com>