[PATCH] iio: adc: stm32-adc: fix runtime autosuspend delay when slow polling

[Fabrice Gasnier]

When the ADC is runtime suspended and starting a conversion, the stm32-adc
driver calls pm_runtime_get_sync() that gets cascaded to the parent
(e.g. runtime resume of stm32-adc-core driver). This also kicks the
autosuspend delay (e.g. 2s) of the parent.
Once the ADC is active, calling pm_runtime_get_sync() again (upon a new
capture) won't kick the autosuspend delay for the parent (stm32-adc-core
driver) as already active.

Currently, this makes the stm32-adc-core driver go in suspend state
every 2s when doing slow polling. As an example, doing a capture, e.g.
cat in_voltageY_raw at a 0.2s rate, the auto suspend delay for the parent
isn't refreshed. Once it expires, the parent immediately falls into
runtime suspended state, in between two captures, as soon as the child
driver falls into runtime suspend state:
- e.g. after 2s, + child calls pm_runtime_put_autosuspend() + 100ms
  autosuspend delay of the child.
- stm32-adc-core switches off regulators, clocks and so on.
- They get switched on back again 100ms later in this example (at 2.2s).

So, add an explicit call to pm_runtime_mark_last_busy() for the parent
driver (stm32-adc-core), synchronously with the child driver (stm32-adc),
to avoid this.

Fixes: 9bdbb1139ca1 ("iio: adc: stm32-adc: add power management support")

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
---
 drivers/iio/adc/stm32-adc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 3b291d7..670157e 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -1157,6 +1157,7 @@ static int stm32_adc_single_conv(struct iio_dev *indio_dev,
 
 	stm32_adc_conv_irq_disable(adc);
 
+	pm_runtime_mark_last_busy(dev->parent);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
 
@@ -1278,6 +1279,7 @@ static int stm32_adc_update_scan_mode(struct iio_dev *indio_dev,
 	adc->num_conv = bitmap_weight(scan_mask, indio_dev->masklength);
 
 	ret = stm32_adc_conf_scan_seq(indio_dev, scan_mask);
+	pm_runtime_mark_last_busy(dev->parent);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
 
@@ -1329,6 +1331,7 @@ static int stm32_adc_debugfs_reg_access(struct iio_dev *indio_dev,
 	else
 		*readval = stm32_adc_readl(adc, reg);
 
+	pm_runtime_mark_last_busy(dev->parent);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
 
@@ -1451,6 +1454,7 @@ static int __stm32_adc_buffer_postenable(struct iio_dev *indio_dev)
 err_clr_trig:
 	stm32_adc_set_trig(indio_dev, NULL);
 err_pm_put:
+	pm_runtime_mark_last_busy(dev->parent);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
 
@@ -1487,6 +1491,7 @@ static void __stm32_adc_buffer_predisable(struct iio_dev *indio_dev)
 	if (stm32_adc_set_trig(indio_dev, NULL))
 		dev_err(&indio_dev->dev, "Can't clear trigger\n");
 
+	pm_runtime_mark_last_busy(dev->parent);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
 }
@@ -1874,6 +1879,7 @@ static int stm32_adc_probe(struct platform_device *pdev)
 		goto err_hw_stop;
 	}
 
+	pm_runtime_mark_last_busy(dev->parent);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
 
-- 
2.7.4