[PATCH v2 2/2] tools/testing/cxl: Enable zero sized decoders under hb0

[Richard Cheng]

The kernel now allows committed HDM decoders of zero size so BIOS can
burn slots with LOCK. Without cxl_test coverage the new path goes
unexercised.

For the special endpoints under host-bridge 0, e.g. cxl_mem.0 and
cxl_mem.4, commit decoders 1 and 2 as zero-size + locked alongside the
existing autoregion at decoder[0]. Mirro the same shape on the parent
switch and host bridge via the walk-up that already builds the
autoregion path.

Signed-off-by: Vishal Aslot <vaslot@xxxxxxxxxx>
Signed-off-by: Richard Cheng <icheng@xxxxxxxxxx>
---
Changelog:

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 instread 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 | 79 +++++++++++++++++++++++++++++++-----
 1 file changed, 69 insertions(+), 10 deletions(-)

diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
index 418669927fb0..1ae0290a9221 100644
--- a/tools/testing/cxl/test/cxl.c
+++ b/tools/testing/cxl/test/cxl.c
@@ -1041,16 +1041,41 @@ 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;
+}
+
+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;
 }
 
 /*
@@ -1123,15 +1148,17 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 	}
 
 	/*
-	 * The first decoder on the first 2 devices on the first switch
-	 * attached to host-bridge0 mock a fake / static RAM region. All
-	 * other decoders are default disabled. Given the round robin
-	 * assignment those devices are named cxl_mem.0, and cxl_mem.4.
+	 * On the first 2 devices on the first switch attached to
+	 * host-bridge0, decoder[0] mocks a fake / static RAM region and
+	 * decoders 1 and 2 mock BIOS-burnt zero-size + locked slots
+	 * (CXL r3.2 §8.2.4.20.12, §14.13.10). All other decoders are
+	 * default disabled. Given the round robin assignment those
+	 * devices are named cxl_mem.0 and cxl_mem.4.
 	 *
 	 * 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 > 2) {
 		default_mock_decoder(cxld);
 		return false;
 	}
@@ -1145,6 +1172,18 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 	base = window->base_hpa;
 	if (extended_linear_cache)
 		base += mock_auto_region_size;
+
+	/*
+	 * Decoders 1 and 2 of the special endpoints under host-bridge0
+	 * are committed as zero-size + locked to mock BIOS burning
+	 * decoder slots (CXL r3.2 §8.2.4.20.12, §14.13.10).
+	 */
+	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 +1207,12 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 	 */
 	iter = port;
 	for (i = 0; i < 2; i++) {
+		int id;
+
 		dport = iter->parent_dport;
 		iter = dport->port;
-		dev = device_find_child(&iter->dev, NULL, first_decoder);
+		id = 0;
+		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 +1256,23 @@ static bool mock_init_hdm_decoder(struct cxl_decoder *cxld)
 
 		cxld_registry_update(cxld);
 		put_device(dev);
+
+		/*
+		 * Mirror the endpoint: also commit the next two switch
+		 * decoders as zero-size + locked so the hierarchy looks
+		 * like a BIOS post-lock layout end-to-end.
+		 */
+		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;
-- 
2.43.0