[PATCH v3 2/2] tools/testing/cxl: Enable zero sized decoder under hb0

[Richard Cheng <icheng@nvidia.com>]

The kernel now allows committed HDM decoders of zero size so BIOS can
burn slots with LOCK, cxl_test needs to exercise the patch.

Add a mock_zero_size_decoders module param, When set, the special
endpoint under host-bridge0 (cxl_mem.0 and cxl_mem.4) commit decoders 1
and 2 as zero-size + locked above the decoder[0] auto-region, mirrored
on the parent switch and host bridge. commit_end then lands on a decoder
with no DPA resource, exercising the new enumeration and
poison-by-endpoint paths.

Signed-off-by: Vishal Aslot <vaslot@nvidia.com>
Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
v2->v3:
      - Gate the zero-size + locked decoder injection behind a new
        mock_zero_size_decoders module parameter (default off). v2 applied
        it unconditionally on the host-bridge0 auto-region endpoints, which
        the region test suite reuses, regressing 7 of 17 cxl unit tests;
        defaulting off leaves the shared topology untouched.

v1->v2:
      - Replace second_decoder(), third_decoder() with a single
        match_decoder_by_index() helper, so all lookups share one matcher.
      - Use DEFINE_RANGE() for the empty range instead of an open-coded
        struct.
      - Set cxled->state = CXL_DECODER_STATE_MANUAL rather than STATE_AUTO.
      - Set CXL_DECODER_F_LOCK on the mock zero-size decoders to model the
        BIOS-burns-slots case.
---
 tools/testing/cxl/test/cxl.c | 83 +++++++++++++++++++++++++++++++++---
 1 file changed, 77 insertions(+), 6 deletions(-)

diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
index 296516eecfd6..190cb18d6932 100644
--- a/tools/testing/cxl/test/cxl.c
+++ b/tools/testing/cxl/test/cxl.c
@@ -17,6 +17,7 @@
 static int interleave_arithmetic;
 static bool extended_linear_cache;
 static bool fail_autoassemble;
+static bool mock_zero_size_decoders;
 
 #define FAKE_QTG_ID	42
 
@@ -1041,16 +1042,47 @@ static void default_mock_decoder(struct cxl_decoder *cxld)
 	WARN_ON_ONCE(!cxld_registry_new(cxld));
 }
 
-static int first_decoder(struct device *dev, const void *data)
+static int match_decoder_by_index(struct device *dev, const void *data)
 {
+	int target_id = *(const int *)data;
 	struct cxl_decoder *cxld;
 
 	if (!is_switch_decoder(dev))
 		return 0;
 	cxld = to_cxl_decoder(dev);
-	if (cxld->id == 0)
-		return 1;
-	return 0;
+	return cxld->id == target_id;
+}
+
+/*
+ * Mock a BIOS-burnt slot: a committed, locked, zero-size decoder
+ * (CXL r3.2 8.2.4.20.12). Gated by the mock_zero_size_decoders module
+ * param so the default cxl_test topology, shared by the region test
+ * suite, is left undisturbed.
+ */
+static void size_zero_mock_decoder_ep(struct cxl_decoder *cxld, u64 base)
+{
+	struct cxl_endpoint_decoder *cxled = to_cxl_endpoint_decoder(&cxld->dev);
+
+	cxld->hpa_range = DEFINE_RANGE(base, base - 1);
+	cxld->interleave_ways = 2;
+	cxld->interleave_granularity = 4096;
+	cxld->target_type = CXL_DECODER_HOSTONLYMEM;
+	cxld->flags = CXL_DECODER_F_ENABLE | CXL_DECODER_F_LOCK;
+	cxled->state = CXL_DECODER_STATE_MANUAL;
+	cxld->commit = mock_decoder_commit;
+	cxld->reset = mock_decoder_reset;
+}
+
+static void size_zero_mock_decoder_sw(struct cxl_decoder *cxld, u64 base,
+				      int level)
+{
+	cxld->flags = CXL_DECODER_F_ENABLE | CXL_DECODER_F_LOCK;
+	cxld->target_type = CXL_DECODER_HOSTONLYMEM;
+	cxld->interleave_ways = level == 0 ? 2 : 1;
+	cxld->interleave_granularity = 4096;
+	cxld->hpa_range = DEFINE_RANGE(base, base - 1);
+	cxld->commit = mock_decoder_commit;
+	cxld->reset = mock_decoder_reset;
 }
 
 /*
@@ -1131,7 +1163,7 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 	 * See 'cxl list -BMPu -m cxl_mem.0,cxl_mem.4'
 	 */
 	if (!is_endpoint_decoder(&cxld->dev) || !hb0 || pdev->id % 4 ||
-	    pdev->id > 4 || cxld->id > 0) {
+	    pdev->id > 4 || cxld->id > (mock_zero_size_decoders ? 2 : 0)) {
 		default_mock_decoder(cxld);
 		return false;
 	}
@@ -1145,6 +1177,20 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 	base = window->base_hpa;
 	if (extended_linear_cache)
 		base += mock_auto_region_size;
+
+	/*
+	 * With mock_zero_size_decoders, decoders 1 and 2 of the special
+	 * endpoints mock BIOS-burnt zero-size + locked slots above the
+	 * decoder[0] auto-region (CXL r3.2 8.2.4.20.12). commit_end then
+	 * points at a decoder with no DPA resource, exercising the
+	 * zero-size enumeration and poison-by-endpoint code paths.
+	 */
+	if (cxld->id == 1 || cxld->id == 2) {
+		size_zero_mock_decoder_ep(cxld, base);
+		port->commit_end = cxld->id;
+		WARN_ON_ONCE(!cxld_registry_new(cxld));
+		return false;
+	}
 	cxld->hpa_range = (struct range) {
 		.start = base,
 		.end = base + mock_auto_region_size - 1,
@@ -1168,9 +1214,11 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 	 */
 	iter = port;
 	for (i = 0; i < 2; i++) {
+		int id = 0;
+
 		dport = iter->parent_dport;
 		iter = dport->port;
-		dev = device_find_child(&iter->dev, NULL, first_decoder);
+		dev = device_find_child(&iter->dev, &id, match_decoder_by_index);
 		/*
 		 * Ancestor ports are guaranteed to be enumerated before
 		 * @port, and all ports have at least one decoder.
@@ -1214,6 +1262,26 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 
 		cxld_registry_update(cxld);
 		put_device(dev);
+
+		if (!mock_zero_size_decoders)
+			continue;
+
+		/*
+		 * Mirror the endpoint: commit the next two switch decoders
+		 * as zero-size + locked so the burnt-slot layout extends
+		 * end-to-end through the switch and host bridge.
+		 */
+		for (id = 1; id <= 2; id++) {
+			dev = device_find_child(&iter->dev, &id,
+						match_decoder_by_index);
+			if (WARN_ON(!dev))
+				continue;
+			cxld = to_cxl_decoder(dev);
+			size_zero_mock_decoder_sw(cxld, base, i);
+			iter->commit_end = id;
+			cxld_registry_update(cxld);
+			put_device(dev);
+		}
 	}
 
 	return false;
@@ -2030,6 +2098,9 @@ module_param(extended_linear_cache, bool, 0444);
 MODULE_PARM_DESC(extended_linear_cache, "Enable extended linear cache support");
 module_param(fail_autoassemble, bool, 0444);
 MODULE_PARM_DESC(fail_autoassemble, "Simulate missing member of an auto-region");
+module_param(mock_zero_size_decoders, bool, 0444);
+MODULE_PARM_DESC(mock_zero_size_decoders,
+		 "Mock BIOS-burnt committed zero-size locked decoders under host-bridge0");
 module_init(cxl_test_init);
 module_exit(cxl_test_exit);
 MODULE_LICENSE("GPL v2");
-- 
2.43.0