powercap/drivers/dtpm: Add API for dynamic thermal power management

On the embedded world, the complexity of the SoC leads to an
increasing number of hotspots which need to be monitored and mitigated
as a whole in order to prevent the temperature to go above the
normative and legally stated 'skin temperature'.

Another aspect is to sustain the performance for a given power budget,
for example virtual reality where the user can feel dizziness if the
GPU performance is capped while a big CPU is processing something
else. Or reduce the battery charging because the dissipated power is
too high compared with the power consumed by other devices.

The userspace is the most adequate place to dynamically act on the
different devices by limiting their power given an application
profile: it has the knowledge of the platform.

These userspace daemons are in charge of the Dynamic Thermal Power
Management (DTPM).

Nowadays, the dtpm daemons are abusing the thermal framework as they
act on the cooling device state to force a specific and arbitrary
state without taking care of the governor decisions. Given the closed
loop of some governors that can confuse the logic or directly enter in
a decision conflict.

As the number of cooling device support is limited today to the CPU
and the GPU, the dtpm daemons have little control on the power
dissipation of the system. The out of tree solutions are hacking
around here and there in the drivers, in the frameworks to have
control on the devices. The common solution is to declare them as
cooling devices.

There is no unification of the power limitation unit, opaque states
are used.

This patch provides a way to create a hierarchy of constraints using
the powercap framework. The devices which are registered as power
limit-able devices are represented in this hierarchy as a tree. They
are linked together with intermediate nodes which are just there to
propagate the constraint to the children.

The leaves of the tree are the real devices, the intermediate nodes
are virtual, aggregating the children constraints and power
characteristics.

Each node have a weight on a 2^10 basis, in order to reflect the
percentage of power distribution of the children's node. This
percentage is used to dispatch the power limit to the children.

The weight is computed against the max power of the siblings.

This simple approach allows to do a fair distribution of the power
limit.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/powercap/Kconfig

@@ -43,4 +43,10 @@ config IDLE_INJECT
 	  CPUs for power capping. Idle period can be injected
 	  synchronously on a set of specified CPUs or alternatively
 	  on a per CPU basis.
+
+config DTPM
+	bool "Power capping for Dynamic Thermal Power Management"
+	help
+	  This enables support for the power capping for the dynamic
+	  thermal power management userspace engine.
 endif

drivers/powercap/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_DTPM) += dtpm.o
 obj-$(CONFIG_POWERCAP)	+= powercap_sys.o
 obj-$(CONFIG_INTEL_RAPL_CORE) += intel_rapl_common.o
 obj-$(CONFIG_INTEL_RAPL) += intel_rapl_msr.o

include/asm-generic/vmlinux.lds.h

@@ -316,6 +316,16 @@
 #define THERMAL_TABLE(name)
 #endif
 
+#ifdef CONFIG_DTPM
+#define DTPM_TABLE()							\
+	. = ALIGN(8);							\
+	__dtpm_table = .;						\
+	KEEP(*(__dtpm_table))						\
+	__dtpm_table_end = .;
+#else
+#define DTPM_TABLE()
+#endif
+
 #define KERNEL_DTB()							\
 	STRUCT_ALIGN();							\
 	__dtb_start = .;						\
@@ -733,6 +743,7 @@
 	ACPI_PROBE_TABLE(irqchip)					\
 	ACPI_PROBE_TABLE(timer)						\
 	THERMAL_TABLE(governor)						\
+	DTPM_TABLE()							\
 	EARLYCON_TABLE()						\
 	LSM_TABLE()							\
 	EARLY_LSM_TABLE()						\

include/linux/dtpm.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Linaro Ltd
+ *
+ * Author: Daniel Lezcano <daniel.lezcano@linaro.org>
+ */
+#ifndef ___DTPM_H__
+#define ___DTPM_H__
+
+#include <linux/powercap.h>
+
+#define MAX_DTPM_DESCR 8
+#define MAX_DTPM_CONSTRAINTS 1
+
+struct dtpm {
+	struct powercap_zone zone;
+	struct dtpm *parent;
+	struct list_head sibling;
+	struct list_head children;
+	struct dtpm_ops *ops;
+	unsigned long flags;
+	u64 power_limit;
+	u64 power_max;
+	u64 power_min;
+	int weight;
+	void *private;
+};
+
+struct dtpm_ops {
+	u64 (*set_power_uw)(struct dtpm *, u64);
+	u64 (*get_power_uw)(struct dtpm *);
+	void (*release)(struct dtpm *);
+};
+
+struct dtpm_descr;
+
+typedef int (*dtpm_init_t)(struct dtpm_descr *);
+
+struct dtpm_descr {
+	struct dtpm *parent;
+	const char *name;
+	dtpm_init_t init;
+};
+
+/* Init section thermal table */
+extern struct dtpm_descr *__dtpm_table[];
+extern struct dtpm_descr *__dtpm_table_end[];
+
+#define DTPM_TABLE_ENTRY(name)			\
+	static typeof(name) *__dtpm_table_entry_##name	\
+	__used __section("__dtpm_table") = &name
+
+#define DTPM_DECLARE(name)	DTPM_TABLE_ENTRY(name)
+
+#define for_each_dtpm_table(__dtpm)	\
+	for (__dtpm = __dtpm_table;	\
+	     __dtpm < __dtpm_table_end;	\
+	     __dtpm++)
+
+static inline struct dtpm *to_dtpm(struct powercap_zone *zone)
+{
+	return container_of(zone, struct dtpm, zone);
+}
+
+int dtpm_update_power(struct dtpm *dtpm, u64 power_min, u64 power_max);
+
+int dtpm_release_zone(struct powercap_zone *pcz);
+
+struct dtpm *dtpm_alloc(struct dtpm_ops *ops);
+
+void dtpm_unregister(struct dtpm *dtpm);
+
+int dtpm_register(const char *name, struct dtpm *dtpm, struct dtpm *parent);
+
+#endif