[PATCH 5.4 151/168] regulator: stm32-vrefbuf: fix a possible overshoot when re-enabling

[Greg Kroah-Hartman]

From: Fabrice Gasnier <fabrice.gasnier@xxxxxx>

commit 02fbabd5f4ed182d2c616e49309f5a3efd9ec671 upstream.

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@xxxxxx>
Message-Id: <1583312132-20932-1-git-send-email-fabrice.gasnier@xxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/regulator/stm32-vrefbuf.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/regulator/stm32-vrefbuf.c
+++ b/drivers/regulator/stm32-vrefbuf.c
@@ -88,7 +88,7 @@ static int stm32_vrefbuf_disable(struct
 	}
 
 	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
 	.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,
 };