[U-Boot] [PATCH 4/5] imx: ventana: use continuous PWM mode and 1MHz for LTC3676 PMIC regulators

[Tim Harvey]

It has been found that the default pulse-skipping mode of the LTC3676
regulators produces noise that the IMX6 is especially susceptible to when
run in ldo-bypass mode.

Switch to continuous PWM mode to provide a cleaner rail, as well as 1MHz
switching frequency for EMI reduction. There is no noticeable drop in
efficiency between pulse-skipping mode and PWM mode in the Ventana IMX6
use case.

Signed-off-by: Tim Harvey <tharvey at gateworks.com>
---
 board/gateworks/gw_ventana/common.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/board/gateworks/gw_ventana/common.c b/board/gateworks/gw_ventana/common.c
index 366ea93..02e27c7 100644
--- a/board/gateworks/gw_ventana/common.c
+++ b/board/gateworks/gw_ventana/common.c
@@ -902,6 +902,12 @@ void setup_pmic(void)
 			pmic_reg_read(p, LTC3676_DVB3B, &reg);
 			reg |= LTC3676_PGOOD_MASK;
 			pmic_reg_write(p, LTC3676_DVB3B, reg);
+
+			/* Use continuous PWM mode, 1Mhz on all regulators */
+			power_ltc3676_swconfig(p, SW1, PWM, PHASE1, F1125KHZ);
+			power_ltc3676_swconfig(p, SW2, PWM, PHASE1, F1125KHZ);
+			power_ltc3676_swconfig(p, SW3, PWM, PHASE1, F1125KHZ);
+			power_ltc3676_swconfig(p, SW4, PWM, PHASE1, F1125KHZ);
 		}
 	}
 }
-- 
1.9.1