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

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 24 Jan 2020 09:26:09 +0100
Fabrice Gasnier <fabrice.gasnier@st.com> wrote:

> 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@st.com>

Hi Fabrice,

Whilst this will clearly work, it seems like a somewhat adhoc solution.
Power management specialists (cc'd):  Is this what we should be doing, or
have Fabrice and I both missed something that we should be doing here?

Thanks,

Jonathan

> ---
>  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);
>