linux-kernel - [PATCH] cxl/acpi: Warn on unsupported platform config detection

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Date: Wed, 19 Jun 2024 14:59:41 +0200
From: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
To: Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	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>,
	linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
Subject: [PATCH] cxl/acpi: Warn on unsupported platform config detection

Each Host Bridge instance has a corresponding CXL Host Bridge Structure
(CHBS) ACPI table that identifies its capabilities. CHBS tables can be
two types: RCRB and CHBCR.

If a Host Bridge is attached to a device that is operating in Restricted
CXL Device Mode (RCD), BIOS publishes an RCRB with the base address of
registers that describe its capabilities.

However, the new (CXL 2.0+) Component registers (e.g., Extended Security
Capability), can only be accessed by means of a base address published
with a CHBCR.

An algorithm to locate a CHBCR associated with an RCRB would be too
invasive to land without some concrete motivation.

Therefore, just print a message to inform of unsupported config.

Count how many different CHBS "Version" types are detected by
cxl_get_chbs_iter(). Then make cxl_get_chbs() print a warning if that sum
is greater than 1.

Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@...ux.intel.com>
---
 drivers/cxl/acpi.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 571069863c62..9e226a65a5ea 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -482,6 +482,7 @@ struct cxl_chbs_context {
 	unsigned long long uid;
 	resource_size_t base;
 	u32 cxl_version;
+	int count;
 };
 
 static int cxl_get_chbs_iter(union acpi_subtable_headers *header, void *arg,
@@ -490,10 +491,17 @@ static int cxl_get_chbs_iter(union acpi_subtable_headers *header, void *arg,
 	struct cxl_chbs_context *ctx = arg;
 	struct acpi_cedt_chbs *chbs;
 
-	if (ctx->base != CXL_RESOURCE_NONE)
+	chbs = (struct acpi_cedt_chbs *) header;
+
+	if (chbs->cxl_version == ACPI_CEDT_CHBS_VERSION_CXL11 &&
+	    chbs->length != CXL_RCRB_SIZE)
 		return 0;
 
-	chbs = (struct acpi_cedt_chbs *) header;
+	if (ctx->cxl_version != chbs->cxl_version)
+		ctx->count++;
+
+	if (ctx->base != CXL_RESOURCE_NONE)
+		return 0;
 
 	if (ctx->uid != chbs->uid)
 		return 0;
@@ -502,10 +510,6 @@ static int cxl_get_chbs_iter(union acpi_subtable_headers *header, void *arg,
 	if (!chbs->base)
 		return 0;
 
-	if (chbs->cxl_version == ACPI_CEDT_CHBS_VERSION_CXL11 &&
-	    chbs->length != CXL_RCRB_SIZE)
-		return 0;
-
 	ctx->base = chbs->base;
 
 	return 0;
@@ -533,6 +537,10 @@ static int cxl_get_chbs(struct device *dev, struct acpi_device *hb,
 
 	acpi_table_parse_cedt(ACPI_CEDT_TYPE_CHBS, cxl_get_chbs_iter, ctx);
 
+	if (ctx->count > 1)
+		/* Disclaim eRCD support given some component register may only be found via CHBCR */
+		dev_info(dev, "Unsupported platform config, mixed Virtual Host and Restricted CXL Host hierarchy.");
+
 	return 0;
 }
 
-- 
2.45.2