intel_adsp: power: dynamic clock switching

This patch adds functionality of a dynamic clock switching by the DSP
during idle.

Signed-off-by: Tomasz Leman <[email protected]>

soc/xtensa/intel_adsp/Kconfig

@@ -120,4 +120,11 @@ config ADSP_CPU_DYNAMIC_CLOCK_GATING
 	  (wait for interrupt) during idle. Clock gating will be disabled in which
 	  there is dependence on dependency to CCOUNT value or DSP clock interrupt.
 
+config ADSP_CPU_DYNAMIC_CLOCK_SWITCHING
+	bool "DSP clock switching in Idle"
+	help
+	  When true, FW will switch clock if all cores are in idle state. The dynamic
+	  clock change is intended to reduce energy consumption when the DSP is waiting
+	  for interrupt.
+
 endif # SOC_FAMILY_INTEL_ADSP

soc/xtensa/intel_adsp/ace/power.c

@@ -381,9 +381,23 @@ void pm_state_exit_post_ops(enum pm_state state, uint8_t substate_id)
 
 #ifdef CONFIG_ARCH_CPU_IDLE_CUSTOM
 
+extern void adsp_clock_idle_entry(void);
+extern void adsp_clock_idle_exit(void);
+
 void arch_cpu_idle(void)
 {
 	sys_trace_idle();
+#if CONFIG_ADSP_CPU_DYNAMIC_CLOCK_SWITCHING
+	/* NOTE: Decreasing a power state lock counter before entering idle. Primary core is
+	 * increasing/decreasing lock counter each time secondary core is powerup/shutdown.
+	 * This way state lock is active for non-idle cores.
+	 */
+	pm_policy_state_lock_put(PM_STATE_ACTIVE, 2);
+
+	if (pm_policy_state_lock_is_active(PM_STATE_ACTIVE, 2)) {
+		adsp_clock_idle_entry();
+	}
+#endif /* CONFIG_ADSP_CPU_DYNAMIC_CLOCK_SWITCHING */
 
 #if CONFIG_ADSP_CPU_DYNAMIC_CLOCK_GATING
 	/* TODO: Add enum for substates (1 -> clock gating) */
@@ -392,9 +406,14 @@ void arch_cpu_idle(void)
 	} else {
 		DSPCS.bootctl[arch_proc_id()].bctl &= ~DSPBR_BCTL_WAITIPCG;
 	}
-#endif
+#endif /* CONFIG_ADSP_CPU_DYNAMIC_CLOCK_GATING */
+
 	wait_for_interrupt(0);
+#if CONFIG_ADSP_CPU_DYNAMIC_CLOCK_SWITCHING
+	pm_policy_state_lock_get(PM_STATE_ACTIVE, 2);
+	adsp_clock_idle_exit();
+#endif /* CONFIG_ADSP_CPU_DYNAMIC_CLOCK_SWITCHING */
 }
-#endif
+#endif /* CONFIG_ARCH_CPU_IDLE_CUSTOM */
 
 #endif

soc/xtensa/intel_adsp/common/clk.c

@@ -153,3 +153,52 @@ uint32_t adsp_clock_source_frequency(int source)
 
 	return adsp_clk_src_info[source].frequency;
 }
+
+#ifdef CONFIG_ADSP_CPU_DYNAMIC_CLOCK_SWITCHING
+/**
+ * @brief Clock change counter.
+ *
+ * A atomic variable that counts how many times the clock has been tried to be lowered.
+ */
+atomic_t clock_change_count;
+
+/**
+ * @brief Clock switch on idle entry.
+ *
+ * This function should be called in Idle thread. Intel ADSP can change clock according to
+ * its needs. But in idle, when core is waiting for interrupt, clock can be change to
+ * lower frequanze.
+ *
+ * @see adsp_clock_idle_exit()
+ */
+void adsp_clock_idle_entry(void)
+{
+	/* we are already at the lowest clock, there is no need to do anything */
+	if (platform_cpu_clocks[0].current_freq != platform_cpu_clocks[0].lowest_freq) {
+		select_cpu_clock_hw(platform_cpu_clocks[0].lowest_freq);
+		(void)atomic_inc(&clock_change_count);
+	}
+}
+
+/**
+ * @brief Clock restore on idle exit.
+ *
+ * This function must be called when exiting the idle state. During idle entry core could switch
+ * clock to the lowest frequency and we need to restore previous settings.
+ *
+ * @see adsp_clock_idle_entry()
+ */
+void adsp_clock_idle_exit(void)
+{
+	/* clock has not been changed */
+	if (!atomic_get(&clock_change_count))
+		return;
+
+	/* If the DSP should run at a higher clock than the lowest, restore this setting */
+	if (platform_cpu_clocks[0].current_freq != platform_cpu_clocks[0].lowest_freq) {
+		select_cpu_clock_hw(platform_cpu_clocks[0].current_freq);
+		(void)atomic_clear(&clock_change_count);
+	}
+}
+
+#endif /* CONFIG_ADSP_CPU_DYNAMIC_CLOCK_SWITCHING */