fan: Enable fan control on AP startup not on shutdown/suspend

There is no need to cool CPU in S3 or S5. We currently don't have fans
for a charging system (i.e. a battery or a charger chip).
Battery management systems control charge current based on its own
temperature readings. Thus, we do not need to keep fans running in S3/S5.

Even with a fan for a charging system, it's questionable to run a fan in
S3/S5. Under a heated condition, spinning a fan would create more heat
as a fan draws current from a battery and the ambient air is hot.

With this patch, EC disables fan control when entering S3/S5 (though fan
control would be already disabled if DPTF is used). It also makes EC
enables fan control when AP starts (for BIOS and OS if DPTF isn't used).

Signee-off-by: Daisuke Nojiri <dnojiri@chromium.org>

BUG=none
BRANCH=none
TEST=Verify fan spins in S0 and stops in S3/S5. Fan is controled by EC
in BIOS and by DPTF in OS after warm and cold reboot.
Run make run-fan.

Change-Id: Idb4610303e65f7fd4d6b24a0dfe511cd629bf6a7
Reviewed-on: https://chromium-review.googlesource.com/1138822
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/1344571
Commit-Queue: Daisuke Nojiri <dnojiri@chromium.org>

2 files changed, 32 insertions, 12 deletions

diff --git a/common/fan.c b/common/fan.c
index 29c7d508a9..46233da715 100644
--- a/common/fan.c
+++ b/common/fan.c
@@ -83,7 +83,7 @@ static void set_enabled(int fan, int enable)
 		gpio_set_level(fans[fan].conf->enable_gpio, enable);
 }
 
-static void set_thermal_control_enabled(int fan, int enable)
+test_export_static void set_thermal_control_enabled(int fan, int enable)
 {
 	thermal_control_enabled[fan] = enable;
 
@@ -454,9 +454,6 @@ static void pwm_fan_init(void)
 				CONFIG_FAN_INIT_SPEED));
 	}
 
-	for (fan = 0; fan < CONFIG_FANS; fan++)
-		set_thermal_control_enabled(fan, 1);
-
 	/* Initialize memory-mapped data */
 	mapped = (uint16_t *)host_get_memmap(EC_MEMMAP_FAN);
 	for (i = 0; i < EC_FAN_SPEED_ENTRIES; i++)
@@ -522,21 +519,40 @@ static void pwm_fan_resume(void)
 }
 DECLARE_HOOK(HOOK_CHIPSET_RESUME, pwm_fan_resume, HOOK_PRIO_DEFAULT);
 
-static void pwm_fan_S3_S5(void)
+static void pwm_fan_startup(void)
+{
+	int fan;
+	/* Turn on fan control when the processor boots up (for BIOS screens) */
+	for (fan = 0; fan < CONFIG_FANS; fan++)
+		set_thermal_control_enabled(fan, 1);
+}
+/* We need to cover cold boot and warm boot. */
+DECLARE_HOOK(HOOK_CHIPSET_STARTUP, pwm_fan_startup, HOOK_PRIO_DEFAULT);
+DECLARE_HOOK(HOOK_CHIPSET_RESET, pwm_fan_startup, HOOK_PRIO_FIRST);
+
+static void pwm_fan_s3_s5(void)
 {
 	int fan;
 
 	/* TODO(crosbug.com/p/23530): Still treating all fans as one. */
 	for (fan = 0; fan < CONFIG_FANS; fan++) {
-		/* Take back fan control when the processor shuts down */
-		set_thermal_control_enabled(fan, 1);
-		/* For now don't do anything with it. We'll have to turn it on
-		 * again if we need active cooling during heavy battery
-		 * charging or something.
+		/*
+		 * There is no need to cool CPU in S3 or S5. We currently don't
+		 * have fans for battery or charger chip. Battery systems will
+		 * control charge current based on its own temperature readings.
+		 * Thus, we do not need to keep fans running in S3 or S5.
+		 *
+		 * Even with a fan on charging system, it's questionable to run
+		 * a fan in S3/S5. Under an extreme heat condition, spinning a
+		 * fan would create more heat as it draws current from a
+		 * battery and heat would come from ambient air instead of CPU.
+		 *
+		 * Thermal control may be already disabled if DPTF is used.
 		 */
+		set_thermal_control_enabled(fan, 0);
 		fan_set_rpm_target(FAN_CH(fan), 0);
 		set_enabled(fan, 0); /* crosbug.com/p/8097 */
 	}
 }
-DECLARE_HOOK(HOOK_CHIPSET_SUSPEND, pwm_fan_S3_S5, HOOK_PRIO_DEFAULT);
-DECLARE_HOOK(HOOK_CHIPSET_SHUTDOWN, pwm_fan_S3_S5, HOOK_PRIO_DEFAULT);
+DECLARE_HOOK(HOOK_CHIPSET_SUSPEND, pwm_fan_s3_s5, HOOK_PRIO_DEFAULT);
+DECLARE_HOOK(HOOK_CHIPSET_SHUTDOWN, pwm_fan_s3_s5, HOOK_PRIO_DEFAULT);
diff --git a/test/fan.c b/test/fan.c
index 6082de1553..c5e4c32fd8 100644
--- a/test/fan.c
+++ b/test/fan.c
@@ -22,6 +22,8 @@
 /*****************************************************************************/
 /* Tests */
 
+void set_thermal_control_enabled(int fan, int enable);
+
 static int test_fan(void)
 {
 	/* "actual" fan speed from board/host/fan.c */
@@ -32,6 +34,8 @@ static int test_fan(void)
 	/* With nothing else to do, fans default to full-on */
 	TEST_ASSERT(fan_get_rpm_actual(0) == FAN_RPM(0)->rpm_max);
 
+	set_thermal_control_enabled(0, 1);
+
 	/*
 	 * fan_set_percent_needed() is normally called once a second by the
 	 * thermal task, but we're not using a thermal test in this test so