For controllers with battery sensing capability (AST2600/AST2700), the
last channel uses a different circuit design optimized for battery
voltage measurement. This channel should not be enabled by default
along with other channels to avoid potential interference and power
efficiency issues.
This ensures optimal power efficiency for normal ADC operations while
maintaining full functionality when battery sensing is needed.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
---
 drivers/iio/adc/aspeed_adc.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c
index 81a2dd752541..ab173d8542c6 100644
--- a/drivers/iio/adc/aspeed_adc.c
+++ b/drivers/iio/adc/aspeed_adc.c
@@ -148,6 +148,13 @@ struct aspeed_adc_data {
 
 static inline unsigned int aspeed_adc_get_active_channels(const struct aspeed_adc_data *data)
 {
+	/*
+	 * For controllers with battery sensing capability, the last channel
+	 * is reserved for battery sensing and should not be included in
+	 * normal channel operations.
+	 */
+	if (data->model_data->bat_sense_sup)
+		return data->model_data->num_channels - 1;
 	return data->model_data->num_channels;
 }
 
@@ -315,9 +322,26 @@ static int aspeed_adc_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
+		adc_engine_control_reg_val = readl(data->base + ASPEED_REG_ENGINE_CONTROL);
+		/*
+		 * For battery sensing capable controllers, we need to enable
+		 * the specific channel before reading. This is required because
+		 * the battery channel may not be enabled by default.
+		 */
+		if (data->model_data->bat_sense_sup &&
+		    chan->channel == ASPEED_ADC_BATTERY_CHANNEL) {
+			u32 ctrl_reg = adc_engine_control_reg_val & ~ASPEED_ADC_CTRL_CHANNEL;
+
+			ctrl_reg |= ASPEED_ADC_CTRL_CHANNEL_ENABLE(chan->channel);
+			writel(ctrl_reg, data->base + ASPEED_REG_ENGINE_CONTROL);
+			/*
+			 * After enable a new channel need to wait some time for adc stable
+			 * Experiment result is 1ms.
+			 */
+			mdelay(1);
+		}
+
 		if (data->battery_sensing && chan->channel == ASPEED_ADC_BATTERY_CHANNEL) {
-			adc_engine_control_reg_val =
-				readl(data->base + ASPEED_REG_ENGINE_CONTROL);
 			writel(adc_engine_control_reg_val |
 				       FIELD_PREP(ASPEED_ADC_CH7_MODE,
 						  ASPEED_ADC_CH7_BAT) |
@@ -331,11 +355,11 @@ static int aspeed_adc_read_raw(struct iio_dev *indio_dev,
 			*val = readw(data->base + chan->address);
 			*val = (*val * data->battery_mode_gain.mult) /
 			       data->battery_mode_gain.div;
-			/* Restore control register value */
-			writel(adc_engine_control_reg_val,
-			       data->base + ASPEED_REG_ENGINE_CONTROL);
 		} else
 			*val = readw(data->base + chan->address);
+		/* Restore control register value */
+		writel(adc_engine_control_reg_val,
+				data->base + ASPEED_REG_ENGINE_CONTROL);
 		return IIO_VAL_INT;
 
 	case IIO_CHAN_INFO_OFFSET:

-- 
2.34.1

On Mon, Mar 16, 2026 at 11:00:48AM +0800, Billy Tsai wrote:
> For controllers with battery sensing capability (AST2600/AST2700), the
> last channel uses a different circuit design optimized for battery
> voltage measurement. This channel should not be enabled by default
> along with other channels to avoid potential interference and power
> efficiency issues.
> This ensures optimal power efficiency for normal ADC operations while
> maintaining full functionality when battery sensing is needed.

...

> +			/*
> +			 * After enable a new channel need to wait some time for adc stable

ADC

> +			 * Experiment result is 1ms.
> +			 */
> +			mdelay(1);

Why atomic? If not required, use fsleep(). Otherwise explain.

> +		}

-- 
With Best Regards,
Andy Shevchenko