[PATCH] cxl: check decoder count for end device

[Dave Jiang <dave.jiang@intel.com>]

CXL spec rev3.0 8.2.4.19.1 added definition for up to 32 decoders. It also
indicates that for devices, only 10 decoders should be advertised. Add
check on number of decoders greater than 10 for devices and reset to 10 to
force spec compliance.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
 drivers/cxl/core/hdm.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index d1d2caea5c62..1919d99d157e 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -71,9 +71,23 @@ EXPORT_SYMBOL_NS_GPL(devm_cxl_add_passthrough_decoder, CXL);
 static void parse_hdm_decoder_caps(struct cxl_hdm *cxlhdm)
 {
 	u32 hdm_cap;
+	int decoder_count;
+	struct device *dev = &cxlhdm->port->dev;
 
 	hdm_cap = readl(cxlhdm->regs.hdm_decoder + CXL_HDM_DECODER_CAP_OFFSET);
-	cxlhdm->decoder_count = cxl_hdm_decoder_count(hdm_cap);
+	decoder_count = cxl_hdm_decoder_count(hdm_cap);
+	/*
+	 * CXL spec rev3.0 8.2.4.19.1 indicates CXL devices shall not advertise
+	 * more than 10 decoders. Switches and Host Bridges may advertise up to
+	 * 32 decoders. Set the decoders to 10 for devices if more than 10 are
+	 * found.
+	 */
+	if (is_cxl_endpoint(cxlhdm->port) && decoder_count > 10) {
+		dev_warn(dev, "Reset decoders count (%d) to 10, spec violation!\n",
+			 decoder_count);
+		decoder_count = 10;
+	}
+	cxlhdm->decoder_count = decoder_count;
 	cxlhdm->target_count =
 		FIELD_GET(CXL_HDM_DECODER_TARGET_COUNT_MASK, hdm_cap);
 	if (FIELD_GET(CXL_HDM_DECODER_INTERLEAVE_11_8, hdm_cap))