[PATCH] power: regulator: stm32: vrefbuf: fix a possible overshoot when re-enabling
From: Fabrice Gasnier fabrice.gasnier@st.com
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 ---
drivers/power/regulator/stm32-vrefbuf.c | 16 ++++++++++++++-- 1 file 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;
Hi Patrick
On 6/12/20 10:40 AM, Patrick Delaunay wrote:
From: Fabrice Gasnier fabrice.gasnier@st.com
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
drivers/power/regulator/stm32-vrefbuf.c | 16 ++++++++++++++-- 1 file 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);
Reviewed-by: Patrice Chotard patrice.chotard@st.com
Thanks
On 7/2/20 4:28 PM, Patrice CHOTARD wrote:
Hi Patrick
On 6/12/20 10:40 AM, Patrick Delaunay wrote:
From: Fabrice Gasnier fabrice.gasnier@st.com
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
drivers/power/regulator/stm32-vrefbuf.c | 16 ++++++++++++++-- 1 file 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);Reviewed-by: Patrice Chotard patrice.chotard@st.com
Reviewed-by: Jaehoon Chung jh80.chung@samsung.com
Thanks
participants (3)
-
Jaehoon Chung -
Patrice CHOTARD -
Patrick Delaunay