From: Dan Williams <dan.j.williams@intel.com>
Date: Fri, 14 Apr 2023 11:54:11 -0700
Subject: [PATCH] cxl/port: Scan single-target ports for decoders
References: bsc#1012628
Patch-mainline: 6.3.2
Git-commit: 7bba261e0aa6e8e5f28a3a3def8338b6512534ee

commit 7bba261e0aa6e8e5f28a3a3def8338b6512534ee upstream.

Do not assume that a single-target port falls back to a passthrough
decoder configuration. Scan for decoders and only fallback after probing
that the HDM decoder capability is not present.

One user visible affect of this bug is the inability to enumerate
present CXL regions as the decoder settings for the present decoders are
skipped.

Fixes: d17d0540a0db ("cxl/core/hdm: Add CXL standard decoder enumeration to the core")
Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: http://lore.kernel.org/r/20230227153128.8164-1-Jonathan.Cameron@huawei.com
Cc: <stable@vger.kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://lore.kernel.org/r/168149845130.792294.3210421233937427962.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/cxl/core/hdm.c |  5 +++--
 drivers/cxl/port.c     | 18 +++++++++++++-----
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 6fdf7981..abe3877c 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -92,8 +92,9 @@ static int map_hdm_decoder_regs(struct cxl_port *port, void __iomem *crb,
 
 	cxl_probe_component_regs(&port->dev, crb, &map.component_map);
 	if (!map.component_map.hdm_decoder.valid) {
-		dev_err(&port->dev, "HDM decoder registers invalid\n");
-		return -ENXIO;
+		dev_dbg(&port->dev, "HDM decoder registers not implemented\n");
+		/* unique error code to indicate no HDM decoder capability */
+		return -ENODEV;
 	}
 
 	return cxl_map_component_regs(&port->dev, regs, &map,
diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
index 22a7ab2b..eb57324c 100644
--- a/drivers/cxl/port.c
+++ b/drivers/cxl/port.c
@@ -66,14 +66,22 @@ static int cxl_switch_port_probe(struct cxl_port *port)
 	if (rc < 0)
 		return rc;
 
-	if (rc == 1)
-		return devm_cxl_add_passthrough_decoder(port);
-
 	cxlhdm = devm_cxl_setup_hdm(port, NULL);
-	if (IS_ERR(cxlhdm))
+	if (!IS_ERR(cxlhdm))
+		return devm_cxl_enumerate_decoders(cxlhdm, NULL);
+
+	if (PTR_ERR(cxlhdm) != -ENODEV) {
+		dev_err(&port->dev, "Failed to map HDM decoder capability\n");
 		return PTR_ERR(cxlhdm);
+	}
+
+	if (rc == 1) {
+		dev_dbg(&port->dev, "Fallback to passthrough decoder\n");
+		return devm_cxl_add_passthrough_decoder(port);
+	}
 
-	return devm_cxl_enumerate_decoders(cxlhdm, NULL);
+	dev_err(&port->dev, "HDM decoder capability not found\n");
+	return -ENXIO;
 }
 
 static int cxl_endpoint_port_probe(struct cxl_port *port)
-- 
2.35.3