[PATCH] accel/rocket: number the cores by devicetree position, not bind order

[Igor Paunovic]

rocket_job_hw_submit() programs the S_POINTER registers of a core with an
extra bit derived from core->index, the way the vendor driver derives it
from the hardware number of the core. rocket_probe() sets core->index to
the slot the core takes in rdev->cores[], which is the order the cores
bind in.

The two agree only while the cores that bind are a prefix of the core
nodes in the devicetree, in devicetree order. Unbind them and bind them
back with a different core first, have one core's probe deferred behind a
sibling's, or disable a core other than the last one, and every task
submitted to a core whose slot is not its hardware number times out after
500 ms. The reset that follows does not help, and the inference finishes
with wrong output.

Observed on an Orange Pi 5 Plus, over all six bind orders of the three
cores: only the devicetree order ran clean. The other five produced 27 to
140 "NPU job timed out" within a single six-second inference, with a
bit-exact oracle rejecting the output, or throughput falling from 130 to
1.95 inferences per second. The timeouts land on the cores whose slot is
not their hardware number, in proportion to the tasks the scheduler hands
them, and in both directions of the mismatch.

Number the cores by their position among the core nodes in the devicetree
instead, which is what the hardware number is.

The wrong value has been assigned since the driver was added, but it only
reached the hardware once the extra bit was introduced, hence the Fixes
tag below.

Fixes: 0810d5ad88a1 ("accel/rocket: Add job submission IOCTL")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Igor Paunovic <royalnet026@xxxxxxxxx>
Assisted-by: LLM sparse checkpatch
---
 drivers/accel/rocket/rocket_core.h |  5 +++++
 drivers/accel/rocket/rocket_drv.c  | 31 +++++++++++++++++++++++++++++-
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/drivers/accel/rocket/rocket_core.h b/drivers/accel/rocket/rocket_core.h
index f6d7382854ca9..46ed8352a79d2 100644
--- a/drivers/accel/rocket/rocket_core.h
+++ b/drivers/accel/rocket/rocket_core.h
@@ -30,6 +30,11 @@
 struct rocket_core {
 	struct device *dev;
 	struct rocket_device *rdev;
+	/*
+	 * Hardware number of the core: its position among the core nodes in
+	 * the devicetree. Not an index into rdev->cores[] - that slot is what
+	 * find_core_for_dev() returns.
+	 */
 	unsigned int index;
 
 	int irq;
diff --git a/drivers/accel/rocket/rocket_drv.c b/drivers/accel/rocket/rocket_drv.c
index 8bbbce594883e..e2cde31443ffa 100644
--- a/drivers/accel/rocket/rocket_drv.c
+++ b/drivers/accel/rocket/rocket_drv.c
@@ -157,10 +157,39 @@ static const struct drm_driver rocket_drm_driver = {
 	.desc			= "rocket DRM",
 };
 
+/*
+ * The extra bit that rocket_job_hw_submit() sets in the S_POINTER registers
+ * is the hardware number of the core, which is its position among the core
+ * nodes in the devicetree: a disabled core keeps its number. The slot a core
+ * takes in rdev->cores[] is the order the cores happened to bind in, and the
+ * two only agree while the cores that bind are a prefix of those nodes, in
+ * devicetree order. Every task submitted to a core whose slot is not its
+ * hardware number then times out.
+ */
+static int rocket_core_hw_index(struct device *dev)
+{
+	struct device_node *np;
+	int index = 0;
+
+	for_each_matching_node(np, dev->driver->of_match_table) {
+		if (np == dev->of_node) {
+			of_node_put(np);
+			return index;
+		}
+		index++;
+	}
+
+	return -ENODEV;
+}
+
 static int rocket_probe(struct platform_device *pdev)
 {
+	int index = rocket_core_hw_index(&pdev->dev);
 	int ret;
 
+	if (index < 0)
+		return index;
+
 	if (rdev == NULL) {
 		/* First core probing, initialize DRM device. */
 		rdev = rocket_device_init(drm_dev, &rocket_drm_driver);
@@ -176,7 +205,7 @@ static int rocket_probe(struct platform_device *pdev)
 
 	rdev->cores[core].rdev = rdev;
 	rdev->cores[core].dev = &pdev->dev;
-	rdev->cores[core].index = core;
+	rdev->cores[core].index = index;
 
 	rdev->num_cores++;
 

base-commit: a9f09b5ea0c3db1e2d4c0f8d3ebdd612d8aa0366
-- 
2.43.0