adc: stm32mp15: add calibration support

Add support of offset and linear calibration for STM32MP15.
The calibration is performed once at probe. The ADC is set in power on
state for calibration. It remains in this state after calibration,
to give to the kernel the opportunity to retrieve calibration data,
directly from the ADC.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>

1 files changed, 116 insertions, 18 deletions

diff --git a/drivers/adc/stm32-adc.c b/drivers/adc/stm32-adc.c
index 85efc119dbf..1fba707c6f7 100644
--- a/drivers/adc/stm32-adc.c
+++ b/drivers/adc/stm32-adc.c
@@ -33,8 +33,11 @@
 #define STM32H7_ADRDY			BIT(0)
 
 /* STM32H7_ADC_CR - bit fields */
+#define STM32H7_ADCAL			BIT(31)
+#define STM32H7_ADCALDIF		BIT(30)
 #define STM32H7_DEEPPWD			BIT(29)
 #define STM32H7_ADVREGEN		BIT(28)
+#define STM32H7_ADCALLIN		BIT(16)
 #define STM32H7_BOOST			BIT(8)
 #define STM32H7_ADSTART			BIT(2)
 #define STM32H7_ADDIS			BIT(1)
@@ -65,47 +68,72 @@ struct stm32_adc {
 	const struct stm32_adc_cfg *cfg;
 };
 
-static int stm32_adc_stop(struct udevice *dev)
+static void stm32_adc_enter_pwr_down(struct udevice *dev)
 {
 	struct stm32_adc *adc = dev_get_priv(dev);
 
-	setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADDIS);
 	clrbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_BOOST);
 	/* Setting DEEPPWD disables ADC vreg and clears ADVREGEN */
 	setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_DEEPPWD);
-	adc->active_channel = -1;
-
-	return 0;
 }
 
-static int stm32_adc_start_channel(struct udevice *dev, int channel)
+static int stm32_adc_exit_pwr_down(struct udevice *dev)
 {
-	struct adc_uclass_plat *uc_pdata = dev_get_uclass_plat(dev);
 	struct stm32_adc_common *common = dev_get_priv(dev_get_parent(dev));
 	struct stm32_adc *adc = dev_get_priv(dev);
 	int ret;
 	u32 val;
 
+	/* return immediately if ADC is not in deep power down mode */
+	if (!(readl(adc->regs + STM32H7_ADC_CR) & STM32H7_DEEPPWD))
+		return 0;
+
 	/* Exit deep power down, then enable ADC voltage regulator */
 	clrbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_DEEPPWD);
 	setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADVREGEN);
+
 	if (common->rate > STM32H7_BOOST_CLKRATE)
 		setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_BOOST);
 
 	/* Wait for startup time */
 	if (!adc->cfg->has_vregready) {
 		udelay(20);
-	} else {
-		ret = readl_poll_timeout(adc->regs + STM32H7_ADC_ISR, val,
-					 val & STM32MP1_VREGREADY,
-					 STM32_ADC_TIMEOUT_US);
-		if (ret < 0) {
-			stm32_adc_stop(dev);
-			dev_err(dev, "Failed to enable vreg: %d\n", ret);
-			return ret;
-		}
+		return 0;
+	}
+
+	ret = readl_poll_timeout(adc->regs + STM32H7_ADC_ISR, val,
+				 val & STM32MP1_VREGREADY,
+				 STM32_ADC_TIMEOUT_US);
+	if (ret < 0) {
+		stm32_adc_enter_pwr_down(dev);
+		dev_err(dev, "Failed to enable vreg: %d\n", ret);
 	}
 
+	return ret;
+}
+
+static int stm32_adc_stop(struct udevice *dev)
+{
+	struct stm32_adc *adc = dev_get_priv(dev);
+
+	setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADDIS);
+	stm32_adc_enter_pwr_down(dev);
+	adc->active_channel = -1;
+
+	return 0;
+}
+
+static int stm32_adc_start_channel(struct udevice *dev, int channel)
+{
+	struct adc_uclass_plat *uc_pdata = dev_get_uclass_plat(dev);
+	struct stm32_adc *adc = dev_get_priv(dev);
+	int ret;
+	u32 val;
+
+	ret = stm32_adc_exit_pwr_down(dev);
+	if (ret < 0)
+		return ret;
+
 	/* Only use single ended channels */
 	writel(0, adc->regs + STM32H7_ADC_DIFSEL);
 
@@ -162,6 +190,64 @@ static int stm32_adc_channel_data(struct udevice *dev, int channel,
 	return 0;
 }
 
+/**
+ * Fixed timeout value for ADC calibration.
+ * worst cases:
+ * - low clock frequency (0.12 MHz min)
+ * - maximum prescalers
+ * Calibration requires:
+ * - 16384 ADC clock cycle for the linear calibration
+ * - 20 ADC clock cycle for the offset calibration
+ *
+ * Set to 100ms for now
+ */
+#define STM32H7_ADC_CALIB_TIMEOUT_US		100000
+
+static int stm32_adc_selfcalib(struct udevice *dev)
+{
+	struct stm32_adc *adc = dev_get_priv(dev);
+	int ret;
+	u32 val;
+
+	/*
+	 * Select calibration mode:
+	 * - Offset calibration for single ended inputs
+	 * - No linearity calibration. Done in next step.
+	 */
+	clrbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADCALDIF | STM32H7_ADCALLIN);
+
+	/* Start calibration, then wait for completion */
+	setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADCAL);
+	ret = readl_poll_sleep_timeout(adc->regs + STM32H7_ADC_CR, val,
+				       !(val & STM32H7_ADCAL), 100,
+				       STM32H7_ADC_CALIB_TIMEOUT_US);
+	if (ret) {
+		dev_err(dev, "calibration failed\n");
+		goto out;
+	}
+
+	/*
+	 * Select calibration mode, then start calibration:
+	 * - Offset calibration for differential input
+	 * - Linearity calibration (needs to be done only once for single/diff)
+	 *   will run simultaneously with offset calibration.
+	 */
+	setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADCALDIF | STM32H7_ADCALLIN);
+
+	/* Start calibration, then wait for completion */
+	setbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADCAL);
+	ret = readl_poll_sleep_timeout(adc->regs + STM32H7_ADC_CR, val,
+				       !(val & STM32H7_ADCAL), 100,
+				       STM32H7_ADC_CALIB_TIMEOUT_US);
+	if (ret)
+		dev_err(dev, "calibration failed\n");
+
+out:
+	clrbits_le32(adc->regs + STM32H7_ADC_CR, STM32H7_ADCALDIF | STM32H7_ADCALLIN);
+
+	return ret;
+}
+
 static int stm32_adc_get_legacy_chan_count(struct udevice *dev)
 {
 	int ret;
@@ -272,7 +358,7 @@ static int stm32_adc_probe(struct udevice *dev)
 	struct adc_uclass_plat *uc_pdata = dev_get_uclass_plat(dev);
 	struct stm32_adc_common *common = dev_get_priv(dev_get_parent(dev));
 	struct stm32_adc *adc = dev_get_priv(dev);
-	int offset;
+	int offset, ret;
 
 	offset = dev_read_u32_default(dev, "reg", -ENODATA);
 	if (offset < 0) {
@@ -287,7 +373,19 @@ static int stm32_adc_probe(struct udevice *dev)
 	uc_pdata->vdd_microvolts = common->vref_uv;
 	uc_pdata->vss_microvolts = 0;
 
-	return stm32_adc_chan_of_init(dev);
+	ret = stm32_adc_chan_of_init(dev);
+	if (ret < 0)
+		return ret;
+
+	ret = stm32_adc_exit_pwr_down(dev);
+	if (ret < 0)
+		return ret;
+
+	ret = stm32_adc_selfcalib(dev);
+	if (ret)
+		stm32_adc_enter_pwr_down(dev);
+
+	return ret;
 }
 
 static const struct adc_ops stm32_adc_ops = {