samus: change fan RPM values, enable fast-start

Updating the fan speeds according to the manufacturer's specs.

The fan vendor recommends that the minimum fan speed be a 20%
duty cycle. Since the built-in fan controller has a tach-based
feedback loop, I'm using the RPM value instead of the duty cycle
(20% is 2286 RPM, according to the vendor).

The vendor also wants a 30% duty cycle to start turning, but the
built-in fan controller provides support for fast-start too. The
controller's minimum fast-start duty cycle is 50%, but it also
has a programmable number of revolutions that it will wait before
backing off.

Holding my ear down close to the fans while they start and stop,
it seems that the minimum 2 revolution start period is sufficient
and provides the least noise. Of course, since I've never had any
problems starting the fans directly at 1000 RPM this noise is a
little more noticeable than that. It's quite possible that the
built-in controller is smart enough to make 1000 RPM work by
bumping the duty cycle up until the fans turn even if the fans
don't like it.

BUG=chrome-os-partner:32892
BRANCH=ToT,samus
TEST=manual

Listen closely and run the EC console "faninfo" command to see
the fans start and stop as the system boots and idles.

Change-Id: I47c9e7cef3f9f4bd815a13032fe10234decd62ed
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/224830
Reviewed-by: Randall Spangler <rspangler@chromium.org>

3 files changed, 27 insertions, 16 deletions

diff --git a/board/samus/board.c b/board/samus/board.c
index 9d2feb93a8..08dae68780 100644
--- a/board/samus/board.c
+++ b/board/samus/board.c
@@ -105,16 +105,16 @@ BUILD_ASSERT(ARRAY_SIZE(pwm_channels) == PWM_CH_COUNT);
 
 /* Physical fans. These are logically separate from pwm_channels. */
 const struct fan_t fans[] = {
-	{.flags = FAN_USE_RPM_MODE,
-	 .rpm_min = 1000,
-	 .rpm_max = 6500,
+	{.flags = FAN_USE_RPM_MODE | FAN_USE_FAST_START,
+	 .rpm_min = 2286,
+	 .rpm_max = 6350,
 	 .ch = 2,
 	 .pgood_gpio = -1,
 	 .enable_gpio = -1,
 	},
-	{.flags = FAN_USE_RPM_MODE,
-	 .rpm_min = 1000,
-	 .rpm_max = 6500,
+	{.flags = FAN_USE_RPM_MODE | FAN_USE_FAST_START,
+	 .rpm_min = 2286,
+	 .rpm_max = 6350,
 	 .ch = 3,
 	 .pgood_gpio = -1,
 	 .enable_gpio = -1,
diff --git a/chip/lm4/fan.c b/chip/lm4/fan.c
index 8ec25bc1f8..1180d51906 100644
--- a/chip/lm4/fan.c
+++ b/chip/lm4/fan.c
@@ -132,7 +132,9 @@ int fan_is_stalled(int ch)
 
 void fan_channel_setup(int ch, unsigned int flags)
 {
-	if (flags & FAN_USE_RPM_MODE) {
+	uint32_t init;
+
+	if (flags & FAN_USE_RPM_MODE)
 		/*
 		 * Configure automatic/feedback mode:
 		 * 0x8000 = bit 15     = auto-restart
@@ -146,8 +148,8 @@ void fan_channel_setup(int ch, unsigned int flags)
 		 *                       (see note at top of file)
 		 * 0x0000 = bit 0      = automatic control
 		 */
-		LM4_FAN_FANCH(ch) = 0x802c;
-	} else {
+		init = 0x802c;
+	else
 		/*
 		 * Configure drive-only mode:
 		 * 0x0000 = bit 15     = no auto-restart
@@ -159,8 +161,17 @@ void fan_channel_setup(int ch, unsigned int flags)
 		 * 0x0000 = bits 3:2   = 1 pulses per revolution
 		 * 0x0001 = bit 0      = manual control
 		 */
-		LM4_FAN_FANCH(ch) = 0x0001;
-	}
+		init = 0x0001;
+
+	if (flags & FAN_USE_FAST_START)
+		/*
+		 * Configure fast-start mode
+		 * 0x0000 = bits 10:8  = start period (2<<0) edges
+		 * 0x0040 = bits 7:6   = fast start at 50% duty
+		 */
+		init |= 0x0040;
+
+	LM4_FAN_FANCH(ch) = init;
 }
 
 static void fan_init(void)
diff --git a/include/fan.h b/include/fan.h
index 0813535592..a8352987d8 100644
--- a/include/fan.h
+++ b/include/fan.h
@@ -21,8 +21,11 @@ struct fan_t {
 	int enable_gpio;
 };
 
-/* Values for the flags field */
-#define FAN_USE_RPM_MODE (1 << 0)
+/* Values for .flags field */
+/*   Enable automatic RPM control using tach input */
+#define FAN_USE_RPM_MODE   (1 << 0)
+/*   Require a higher duty cycle to start up than to keep running */
+#define FAN_USE_FAST_START (1 << 1)
 
 /* The list of fans is instantiated in board.c. */
 extern const struct fan_t fans[];
@@ -82,9 +85,6 @@ enum fan_status {
 };
 enum fan_status fan_get_status(int ch);
 
-/* Flag to enable automatic RPM control using tach input */
-#define FAN_USE_RPM_MODE (1 << 0)
-
 /* Initialize the HW according to the desired flags */
 void fan_channel_setup(int ch, unsigned int flags);