[PATCH 6/7] accel/rocket: register a devfreq cooling device

[Igor Paunovic]

With devfreq driving the NPU clock, a thermal zone can now throttle the NPU
by capping that clock. Register the cooling device so a devicetree can bind
it to a zone.

The _em variant is used, not because there is an energy model today but so
that there will be one the day a power coefficient for this NPU is
measured. There is none now: the NPU node carries no
dynamic-power-coefficient, Rockchip does not publish one, and a made-up
number would be worse than no number. devfreq_cooling_em_register() logs
the missing model at debug level and registers the cooling device anyway,
so what this gets today is step-wise throttling with no power model for the
IPA governor to use. Measuring the coefficient is follow-up work.

Registration is allowed to fail. A kernel built without DEVFREQ_THERMAL
gets a stub that returns an error, and losing throttling is not a reason to
refuse to drive the NPU at all, so the failure is logged and probe carries
on. The cooling device is unregistered by hand before the devfreq device it
is attached to goes away.

Signed-off-by: Igor Paunovic <royalnet026@xxxxxxxxx>
Assisted-by: LLM sparse checkpatch
---
 drivers/accel/rocket/rocket_devfreq.c | 24 ++++++++++++++++++++++++
 drivers/accel/rocket/rocket_devfreq.h |  2 ++
 2 files changed, 26 insertions(+)

diff --git a/drivers/accel/rocket/rocket_devfreq.c b/drivers/accel/rocket/rocket_devfreq.c
index 9d923a0b6ea30..86bc34819a187 100644
--- a/drivers/accel/rocket/rocket_devfreq.c
+++ b/drivers/accel/rocket/rocket_devfreq.c
@@ -3,6 +3,7 @@
 
 #include <linux/clk.h>
 #include <linux/devfreq.h>
+#include <linux/devfreq_cooling.h>
 #include <linux/ktime.h>
 #include <linux/minmax.h>
 #include <linux/of.h>
@@ -404,6 +405,24 @@ int rocket_devfreq_init(struct rocket_device *rdev)
 		goto err_remove_table;
 	}
 
+	/*
+	 * Thermal throttling is optional, so a kernel built without
+	 * DEVFREQ_THERMAL keeps a working NPU rather than a failed probe.
+	 *
+	 * The _em variant is used so that the driver is ready for an energy
+	 * model the day a power coefficient for this NPU is measured. There is
+	 * none today: the NPU node has no dynamic-power-coefficient, the vendor
+	 * does not publish one, and inventing a number would be worse than
+	 * having none. Without it the EM registration inside is skipped and
+	 * throttling is step-wise, with no power model for IPA to use.
+	 */
+	rdevfreq->cooling = devfreq_cooling_em_register(rdevfreq->devfreq, NULL);
+	if (IS_ERR(rdevfreq->cooling)) {
+		dev_info(dev, "no devfreq cooling device (%pe), NPU will not be throttled\n",
+			 rdevfreq->cooling);
+		rdevfreq->cooling = NULL;
+	}
+
 	return 0;
 
 err_remove_table:
@@ -426,6 +445,11 @@ void rocket_devfreq_fini(struct rocket_device *rdev)
 
 	dev = rdevfreq->owner->dev;
 
+	if (rdevfreq->cooling) {
+		devfreq_cooling_unregister(rdevfreq->cooling);
+		rdevfreq->cooling = NULL;
+	}
+
 	devfreq_remove_device(rdevfreq->devfreq);
 	rdevfreq->devfreq = NULL;
 
diff --git a/drivers/accel/rocket/rocket_devfreq.h b/drivers/accel/rocket/rocket_devfreq.h
index bdf8e89ed3761..d5876d62a0b7c 100644
--- a/drivers/accel/rocket/rocket_devfreq.h
+++ b/drivers/accel/rocket/rocket_devfreq.h
@@ -10,9 +10,11 @@
 
 struct rocket_core;
 struct rocket_device;
+struct thermal_cooling_device;
 
 struct rocket_devfreq {
 	struct devfreq *devfreq;
+	struct thermal_cooling_device *cooling;
 	struct devfreq_simple_ondemand_data gov_data;
 
 	/*
-- 
2.43.0