[PATCH v16 18/18] cxl: Add KUnit checks for HDM decoder unpacking

[Srirangan Madhavan <smadhavan@nvidia.com>]

Test cxl_hdm_unpack_decoder() without a PCI device or HDM MMIO. Cover
range boundaries and overflow, an all-ones base, zero-size and uncommitted
decoders, and a locked host-only decoder with 12-way interleave.

Run the checks as a KUnit suite rather than during cxl_test module loading,
so a failure does not prevent unrelated CXL mock tests from running. An
uncommitted decoder has no meaningful target type, so do not check it.

Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
 drivers/cxl/.kunitconfig             |  4 ++
 drivers/cxl/Kconfig                  | 10 ++++
 drivers/cxl/Makefile                 |  1 +
 drivers/cxl/core/hdm_regs.c          |  2 +-
 drivers/cxl/tests/Makefile           |  5 ++
 drivers/cxl/tests/hdm_unpack_kunit.c | 90 ++++++++++++++++++++++++++++
 6 files changed, 111 insertions(+), 1 deletion(-)
 create mode 100644 drivers/cxl/.kunitconfig
 create mode 100644 drivers/cxl/tests/Makefile
 create mode 100644 drivers/cxl/tests/hdm_unpack_kunit.c

diff --git a/drivers/cxl/.kunitconfig b/drivers/cxl/.kunitconfig
new file mode 100644
index 000000000000..4fee684f5ff6
--- /dev/null
+++ b/drivers/cxl/.kunitconfig
@@ -0,0 +1,4 @@
+CONFIG_KUNIT=y
+CONFIG_PCI=y
+CONFIG_CXL_BUS=y
+CONFIG_CXL_KUNIT_TEST=y
diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index e927e69a3f7b..7f70f6babd74 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -213,6 +213,16 @@ config CXL_REGION
 
 	  If unsure say 'y'
 
+config CXL_KUNIT_TEST
+	tristate "KUnit tests for CXL" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  Build the KUnit tests for the CXL subsystem. When built as modules,
+	  each test suite is its own module.
+
+	  If unsure, say N.
+
 config CXL_REGION_INVALIDATION_TEST
 	bool "CXL: Region Cache Management Bypass (TEST)"
 	depends on CXL_REGION
diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
index 2caa90fa4bf2..d57fb0e9e7da 100644
--- a/drivers/cxl/Makefile
+++ b/drivers/cxl/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
 obj-$(CONFIG_CXL_PMEM) += cxl_pmem.o
 obj-$(CONFIG_CXL_MEM) += cxl_mem.o
 obj-$(CONFIG_CXL_PCI) += cxl_pci.o
+obj-$(CONFIG_CXL_KUNIT_TEST) += tests/
 
 cxl_port-y := port.o
 cxl_acpi-y := acpi.o
diff --git a/drivers/cxl/core/hdm_regs.c b/drivers/cxl/core/hdm_regs.c
index fe5e65a9ddb1..ef1b0e07c352 100644
--- a/drivers/cxl/core/hdm_regs.c
+++ b/drivers/cxl/core/hdm_regs.c
@@ -174,7 +174,7 @@ int cxl_hdm_unpack_decoder(struct cxl_decoder_config *config, int id,
 
 	return 0;
 }
-EXPORT_SYMBOL_FOR_MODULES(cxl_hdm_unpack_decoder, "cxl_core");
+EXPORT_SYMBOL_FOR_MODULES(cxl_hdm_unpack_decoder, "cxl_core,cxl_hdm_unpack_kunit");
 
 int cxl_hdm_read_decoder(struct cxl_decoder_config *config, void __iomem *hdm,
 			 int id, u32 ctrl)
diff --git a/drivers/cxl/tests/Makefile b/drivers/cxl/tests/Makefile
new file mode 100644
index 000000000000..c29dccfa9b24
--- /dev/null
+++ b/drivers/cxl/tests/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+ccflags-y += -I$(srctree)/drivers/cxl
+
+obj-$(CONFIG_CXL_KUNIT_TEST) += cxl_hdm_unpack_kunit.o
+cxl_hdm_unpack_kunit-y := hdm_unpack_kunit.o
diff --git a/drivers/cxl/tests/hdm_unpack_kunit.c b/drivers/cxl/tests/hdm_unpack_kunit.c
new file mode 100644
index 000000000000..6e5b59ef6309
--- /dev/null
+++ b/drivers/cxl/tests/hdm_unpack_kunit.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2026 NVIDIA Corporation & Affiliates */
+#include <kunit/test.h>
+#include <linux/bitfield.h>
+#include <linux/sizes.h>
+
+#include "cxl.h"
+#include "../core/core.h"
+
+static void cxl_hdm_unpack_test(struct kunit *test)
+{
+	static const struct {
+		const char *name;
+		u32 ctrl;
+		u64 base;
+		u64 size;
+		int rc;
+		unsigned long flags;
+		int ways;
+		int granularity;
+		enum cxl_decoder_type target_type;
+	} cases[] = {
+		{ "valid", CXL_HDM_DECODER0_CTRL_COMMITTED,
+		  SZ_1G, SZ_256M, 0, CXL_DECODER_F_ENABLE,
+		  1, 256, CXL_DECODER_DEVMEM },
+		{ "overflow", CXL_HDM_DECODER0_CTRL_COMMITTED,
+		  U64_MAX - 127, 256, -ENXIO },
+		{ "all-ones base", CXL_HDM_DECODER0_CTRL_COMMITTED,
+		  U64_MAX, SZ_256M, -ENXIO },
+		{ "last address", CXL_HDM_DECODER0_CTRL_COMMITTED,
+		  U64_MAX - 255, 256, 0, CXL_DECODER_F_ENABLE,
+		  1, 256, CXL_DECODER_DEVMEM },
+		{ "zero size", CXL_HDM_DECODER0_CTRL_COMMITTED,
+		  SZ_1G, 0, 0, CXL_DECODER_F_ENABLE,
+		  1, 256, CXL_DECODER_DEVMEM },
+		{ "uncommitted stale size", 0,
+		  SZ_1G, SZ_256M, 0, 0, 1, 256 },
+		{ "locked host-only interleave",
+		  CXL_HDM_DECODER0_CTRL_COMMITTED | CXL_HDM_DECODER0_CTRL_LOCK |
+		  CXL_HDM_DECODER0_CTRL_HOSTONLY |
+		  FIELD_PREP_CONST(CXL_HDM_DECODER0_CTRL_IW_MASK, 10) |
+		  FIELD_PREP_CONST(CXL_HDM_DECODER0_CTRL_IG_MASK, 2),
+		  SZ_1G, SZ_256M, 0, CXL_DECODER_F_ENABLE | CXL_DECODER_F_LOCK,
+		  12, SZ_1K, CXL_DECODER_HOSTONLYMEM },
+	};
+
+	for (int i = 0; i < ARRAY_SIZE(cases); i++) {
+		struct cxl_decoder_config config;
+		u64 size;
+		int rc;
+
+		rc = cxl_hdm_unpack_decoder(&config, 3, cases[i].ctrl,
+					    cases[i].base, cases[i].size);
+		KUNIT_EXPECT_EQ_MSG(test, rc, cases[i].rc, "%s", cases[i].name);
+		if (rc || rc != cases[i].rc)
+			continue;
+		size = cases[i].size;
+		if (!(cases[i].flags & CXL_DECODER_F_ENABLE))
+			size = 0;
+		KUNIT_EXPECT_EQ_MSG(test, config.id, 3, "%s", cases[i].name);
+		KUNIT_EXPECT_EQ_MSG(test, config.hpa_range.start, cases[i].base,
+				    "%s", cases[i].name);
+		KUNIT_EXPECT_EQ_MSG(test, range_len(&config.hpa_range), size,
+				    "%s", cases[i].name);
+		KUNIT_EXPECT_EQ_MSG(test, config.flags, cases[i].flags,
+				    "%s", cases[i].name);
+		KUNIT_EXPECT_EQ_MSG(test, config.interleave_ways, cases[i].ways,
+				    "%s", cases[i].name);
+		KUNIT_EXPECT_EQ_MSG(test, config.interleave_granularity,
+				    cases[i].granularity, "%s", cases[i].name);
+		/* An uncommitted decoder has no meaningful target type. */
+		if (cases[i].flags & CXL_DECODER_F_ENABLE)
+			KUNIT_EXPECT_EQ_MSG(test, config.target_type,
+					    cases[i].target_type, "%s", cases[i].name);
+	}
+}
+
+static struct kunit_case cxl_hdm_test_cases[] = {
+	KUNIT_CASE(cxl_hdm_unpack_test),
+	{}
+};
+
+static struct kunit_suite cxl_hdm_test_suite = {
+	.name = "cxl-hdm-unpack",
+	.test_cases = cxl_hdm_test_cases,
+};
+kunit_test_suite(cxl_hdm_test_suite);
+
+MODULE_DESCRIPTION("KUnit tests for CXL HDM decoder unpacking");
+MODULE_LICENSE("GPL");
-- 
2.43.0