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

There maybe an overshoot, when disabling, then re-enabling vrefbuf
too quickly. VREFBUF is used by ADC/DAC on some boards. When re-enabling
too quickly, an overshoot on the reference voltage make the conversions
inaccurate for a short period of time.
- Don't put the VREFBUF in HiZ when disabling, to force an active
discharge.
- Enforce a 1ms OFF/ON delay

Fixes: 0cdbf481e927 ("regulator: Add support for stm32-vrefbuf")

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Message-Id: <1583312132-20932-1-git-send-email-fabrice.gasnier@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/regulator/stm32-vrefbuf.c b/drivers/regulator/stm32-vrefbuf.c
index bdfaf7e..992bc18 100644 (file)
--- a/drivers/regulator/stm32-vrefbuf.c
+++ b/drivers/regulator/stm32-vrefbuf.c
@@ -88,7 +88,7 @@ static int stm32_vrefbuf_disable(struct regulator_dev *rdev)
        }
 
        val = readl_relaxed(priv->base + STM32_VREFBUF_CSR);
-       val = (val & ~STM32_ENVR) | STM32_HIZ;
+       val &= ~STM32_ENVR;
        writel_relaxed(val, priv->base + STM32_VREFBUF_CSR);
 
        pm_runtime_mark_last_busy(priv->dev);
@@ -175,6 +175,7 @@ static const struct regulator_desc stm32_vrefbuf_regu = {
        .volt_table = stm32_vrefbuf_voltages,
        .n_voltages = ARRAY_SIZE(stm32_vrefbuf_voltages),
        .ops = &stm32_vrefbuf_volt_ops,
+       .off_on_delay = 1000,
        .type = REGULATOR_VOLTAGE,
        .owner = THIS_MODULE,
 };