diff options
| author | Fabrice Gasnier <fabrice.gasnier@st.com> | 2020-06-12 11:40:58 +0300 |
|---|---|---|
| committer | Patrick Delaunay <patrick.delaunay@st.com> | 2020-07-07 17:01:23 +0300 |
| commit | 8b8c99bd3e1e9463e27ccd1bca18f4a7627901aa (patch) | |
| tree | 8761e330a836dfa3a6f384acdfab32d811bbad74 /drivers/power | |
| parent | 2ee5005dea1a12bba096abac1f8ebeaea91bf964 (diff) | |
| download | u-boot-8b8c99bd3e1e9463e27ccd1bca18f4a7627901aa.tar.xz | |
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.c | 16 |
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; |