[PATCH v1 1/1] cxl/hdm: Verify HDM decoder capabilities after parsing

[Li Ming <ming.li@zohomail.com>]

devm_cxl_setup_hdm() only checks if decoder_count is 0 after parsing HDM
decoder capability, But according to the implementation of
cxl_hdm_decoder_count(), cxlhdm->decoder_count will never be 0.

Per CXL specification, the values ranges of decoder_count and
target_count are limited. Adding a checking for the values of them
in case hardware initialized them with wrong values.

Signed-off-by: Li Ming <ming.li@zohomail.com>
---
base-commit: 22eea823f69ae39dc060c4027e8d1470803d2e49 cxl/next
---
 drivers/cxl/core/hdm.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 70cae4ebf8a4..a98191867c22 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -138,6 +138,34 @@ static bool should_emulate_decoders(struct cxl_endpoint_dvsec_info *info)
 	return true;
 }
 
+static int cxlhdm_decoder_caps_verify(struct cxl_hdm *cxlhdm)
+{
+	/*
+	 * CXL r3.2 section 8.2.4.20.1
+	 * CXL devices shall not advertise more than 10 decoders,
+	 * CXL switches and HBs may advertise up to 32 decoders.
+	 */
+	if (is_cxl_endpoint(cxlhdm->port) && cxlhdm->decoder_count > 10)
+		return -EINVAL;
+	else if (cxlhdm->decoder_count > 32)
+		return -EINVAL;
+
+	/*
+	 * CXL r3.2 section 8.2.4.20.1
+	 * target count is applicable only to CXL upstream port and HB.
+	 * The number of target ports each decoder supports should be
+	 * one of the numbers 1, 2, 4 or 8.
+	 */
+	if (!is_cxl_endpoint(cxlhdm->port) &&
+	    cxlhdm->target_count != 1 &&
+	    cxlhdm->target_count != 2 &&
+	    cxlhdm->target_count != 4 &&
+	    cxlhdm->target_count != 8)
+		return -EINVAL;
+
+	return 0;
+}
+
 /**
  * devm_cxl_setup_hdm - map HDM decoder component registers
  * @port: cxl_port to map
@@ -182,7 +210,8 @@ struct cxl_hdm *devm_cxl_setup_hdm(struct cxl_port *port,
 	}
 
 	parse_hdm_decoder_caps(cxlhdm);
-	if (cxlhdm->decoder_count == 0) {
+	rc = cxlhdm_decoder_caps_verify(cxlhdm);
+	if (rc) {
 		dev_err(dev, "Spec violation. Caps invalid\n");
 		return ERR_PTR(-ENXIO);
 	}
-- 
2.34.1