power: regulator: stm32: vrefbuf: fix a possible overshoot when re-enabling

[platform/kernel/u-boot.git] / drivers / power / regulator / stm32-vrefbuf.c

diff --git a/drivers/power/regulator/stm32-vrefbuf.c b/drivers/power/regulator/stm32-vrefbuf.c
index 08a10f0..9213696 100644 (file)
--- a/drivers/power/regulator/stm32-vrefbuf.c
+++ b/drivers/power/regulator/stm32-vrefbuf.c
@@ -11,6 +11,7 @@
 #include <dm.h>
 #include <asm/io.h>
 #include <dm/device_compat.h>
+#include <linux/bitops.h>
 #include <linux/iopoll.h>
 #include <linux/kernel.h>
 #include <power/regulator.h>
@@ -42,8 +43,20 @@ static int stm32_vrefbuf_set_enable(struct udevice *dev, bool enable)
        u32 val;
        int ret;
 
-       clrsetbits_le32(priv->base + STM32_VREFBUF_CSR, STM32_HIZ | STM32_ENVR,
-                       enable ? STM32_ENVR : STM32_HIZ);
+       if (enable && !(readl(priv->base + STM32_VREFBUF_CSR) & STM32_ENVR)) {
+               /*
+                * There maybe an overshoot:
+                * - when disabling, then re-enabling vrefbuf too quickly
+                * - or upon platform reset as external capacitor maybe slow
+                *   discharging (VREFBUF is HiZ at reset by default).
+                * So force active discharge (HiZ=0) for 1ms before enabling.
+                */
+               clrbits_le32(priv->base + STM32_VREFBUF_CSR, STM32_HIZ);
+               udelay(1000);
+       }
+
+       clrsetbits_le32(priv->base + STM32_VREFBUF_CSR, STM32_ENVR,
+                       enable ? STM32_ENVR : 0);
        if (!enable)
                return 0;