linux-kernel - [PATCH v1 04/29] cxl/pci: Add comments to cxl_hdm_decode

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Message-ID: <20250107141015.3367194-5-rrichter@amd.com>
Date: Tue, 7 Jan 2025 15:09:50 +0100
From: Robert Richter <rrichter@....com>
To: Alison Schofield <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Dan Williams
	<dan.j.williams@...el.com>, Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>, Davidlohr Bueso <dave@...olabs.net>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Gregory Price
	<gourry@...rry.net>, "Fabio M. De Francesco"
	<fabio.m.de.francesco@...ux.intel.com>, Terry Bowman <terry.bowman@....com>,
	Robert Richter <rrichter@....com>
Subject: [PATCH v1 04/29] cxl/pci: Add comments to cxl_hdm_decode_init()

There are various configuration cases of HDM decoder registers causing
different code paths. Add comments to cxl_hdm_decode_init() to better
explain them.

Signed-off-by: Robert Richter <rrichter@....com>
---
 drivers/cxl/core/pci.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index c7050c13f71a..4d2154457efb 100644
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -416,9 +416,17 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
 	if (global_ctrl & CXL_HDM_DECODER_ENABLE || (!hdm && info->mem_enabled))
 		return devm_cxl_enable_mem(&port->dev, cxlds);
 
+	/*
+	 * If the HDM Decoder Capability does not exist and DVSEC was
+	 * not setup, the DVSEC based emulation cannot be used.
+	 */
 	if (!hdm)
 		return -ENODEV;
 
+	/*
+	 * The HDM Decoder Capability exists but is globally disabled.
+	 */
+
 	/*
 	 * Per CXL 2.0 Section 8.1.3.8.3 and 8.1.3.8.4 DVSEC CXL Range 1 Base
 	 * [High,Low] when HDM operation is enabled the range register values
@@ -426,7 +434,8 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
 	 * DVSEC Range 1,2 to HDM Decoder Range 0,1. So, non-zero info->ranges
 	 * are expected even though Linux does not require or maintain that
 	 * match. If at least one DVSEC range is enabled and allowed, skip HDM
-	 * Decoder Capability Enable.
+	 * Decoder Capability Enable. Else, use the HDM Decoder Capability and
+	 * enable it.
 	 */
 	if (!info->mem_enabled) {
 		rc = devm_cxl_enable_hdm(&port->dev, cxlhdm);
-- 
2.39.5