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authorFabrice Gasnier <fabrice.gasnier@st.com>2020-06-12 10:40:58 +0200
committerPatrick Delaunay <patrick.delaunay@st.com>2020-07-07 16:01:23 +0200
commit8b8c99bd3e1e9463e27ccd1bca18f4a7627901aa (patch)
tree8761e330a836dfa3a6f384acdfab32d811bbad74 /drivers/power
parent2ee5005dea1a12bba096abac1f8ebeaea91bf964 (diff)
power: regulator: stm32: vrefbuf: fix a possible overshoot when re-enabling
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). VREFBUF is used by ADC/DAC on some boards. An overshoot on the reference voltage make the conversions inaccurate for a short period of time. So: - Don't put the VREFBUF in HiZ when disabling, to force an active discharge. - Enforce a 1ms OFF/ON delay, also upon reset Penalty is a 1ms delay is applied (even for a cold boot), when enabling VREFBUF. Fixes: 93cf0ae7758d ("power: regulator: Add support for stm32-vrefbuf") Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com> Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com> Reviewed-by: Patrice Chotard <patrice.chotard@st.com> Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Diffstat (limited to 'drivers/power')
-rw-r--r--drivers/power/regulator/stm32-vrefbuf.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/drivers/power/regulator/stm32-vrefbuf.c b/drivers/power/regulator/stm32-vrefbuf.c
index 250773514f..92136961c2 100644
--- a/drivers/power/regulator/stm32-vrefbuf.c
+++ b/drivers/power/regulator/stm32-vrefbuf.c
@@ -43,8 +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;