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Date: Wed, 12 Feb 2020 15:02:37 +0100
From: Fabrice Gasnier <fabrice.gasnier@...com>
To: Jonathan Cameron <jic23@...nel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>
CC: <linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <mcoquelin.stm32@...il.com>,
<alexandre.torgue@...com>, <olivier.moysan@...com>,
<linux-iio@...r.kernel.org>, <lars@...afoo.de>, <knaack.h@....de>,
<pmeerw@...erw.net>, <linux-stm32@...md-mailman.stormreply.com>,
<linux-pm@...r.kernel.org>, <ulf.hansson@...aro.org>,
<khilman@...nel.org>
Subject: Re: [PATCH] iio: adc: stm32-adc: fix runtime autosuspend delay when
slow polling
On 2/2/20 4:33 PM, Jonathan Cameron wrote:
> On Fri, 24 Jan 2020 09:26:09 +0100
> Fabrice Gasnier <fabrice.gasnier@...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@...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?
Hi all, PM specialists,
As per my understanding, pm_runtime_mark_last_busy() doesn't cascade to
the parent device:
- in pm_runtime.h:
static inline void pm_runtime_mark_last_busy(struct device *dev)
{
WRITE_ONCE(dev->power.last_busy, ktime_get_mono_fast_ns());
}
STM32 ADC driver uses a model with an autosupsend delay for
- a parent driver to handle common resources, registers etc.
- child drivers for each ADC.
So the question is on how to fix the behavior I described:
1: Child activity with "short" autosuspend_delay
2: Parent activity with "longer" autosuspend_delay
_ _ _ _ _ _ _ _
1: _| |___| |___| |___| |___| |_..._| |___| |___| |_...
v v v v v v v v v v ... v v v v v v
| | | |
| +- pm_runtime_mark_last_busy() | |
| +- pm_runtime_put_autosuspend() v |
| | |
+--- pm_runtime_get_sync() | v
| | |
+---> expires after autosuspend_delay | |
| | |
v v v
_______________________________________ ___...
2: _| ... |___|
Glitches on parent dev near autosuspend_delay ^
- does the child driver needs to "kick" parent driver with
pm_runtime_mark_last_busy(), as proposed in current patch ?
- or is it something that should be done by PM runtime core routines ?
e.g. make pm_runtime_mark_last_busy() recursive or something else ?
Please advise
Best regards,
Fabrice
>
> 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);
>>
>
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