linux-kernel - Re: [PATCH] iio: adc: stm32: fix a leak by resetting pcsel before disabling vdda

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Message-ID: <76ac386a-a748-f044-13c5-46b164738338@foss.st.com>
Date:   Mon, 25 Oct 2021 09:43:10 +0200
From:   Fabrice Gasnier <fabrice.gasnier@...s.st.com>
To:     Jonathan Cameron <jic23@...nel.org>,
        Olivier MOYSAN <olivier.moysan@...s.st.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <alexandre.torgue@...s.st.com>,
        <linux-iio@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH] iio: adc: stm32: fix a leak by resetting pcsel before
 disabling vdda

On 10/24/21 6:07 PM, Jonathan Cameron wrote:
> On Fri, 22 Oct 2021 14:38:52 +0200
> Olivier MOYSAN <olivier.moysan@...s.st.com> wrote:
> 
> I'll probably reword the description here as 'leak' tends to mean memory
> leak rather than current.

Hi Jonathan,

Yes, please fell free to improve this. I had the same concern, but I
haven't found a more suitable description.

> 
>> Hi Fabrice,
>>
>> On 10/22/21 2:19 PM, Fabrice Gasnier wrote:
>>> Some I/Os are connected to ADC input channels, when the corresponding bit
>>> in PCSEL register are set on STM32H7 and STM32MP15. This is done in the
>>> prepare routine of stm32-adc driver.
>>> There are constraints here, as PCSEL shouldn't be set when VDDA supply
>>> is disabled. Enabling/disabling of VDDA supply in done via stm32-adc-core
>>> runtime PM routines (before/after ADC is enabled/disabled).
>>>
>>> Currently, PCSEL remains set when disabling ADC. Later on, PM runtime
>>> can disable the VDDA supply. This creates some conditions on I/Os that
>>> can start to leak current.
>>> So PCSEL needs to be cleared when disabling the ADC.
>>>
>>> Fixes: 95e339b6e85d ("iio: adc: stm32: add support for STM32H7")
>>>
> 
> No line break here as Fixes forms part of the tag block.
> 

Sorry, will check this next time.

>>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...s.st.com>
> 
> Given timing wrt to being too near merge window, I'll let this it on
> list a while longer as it'll be post rc1 material now anyway.
> 
> I can fix the above whilst applying if nothing else comes up.

That's fine for me.

Many thanks,
Fabrice
> 
> Jonathan
> 
>>> ---
>>>   drivers/iio/adc/stm32-adc.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
>>> index 5088de8..e3e7541 100644
>>> --- a/drivers/iio/adc/stm32-adc.c
>>> +++ b/drivers/iio/adc/stm32-adc.c
>>> @@ -975,6 +975,7 @@ static void stm32h7_adc_unprepare(struct iio_dev *indio_dev)
>>>   {
>>>   	struct stm32_adc *adc = iio_priv(indio_dev);
>>>   
>>> +	stm32_adc_writel(adc, STM32H7_ADC_PCSEL, 0);
>>>   	stm32h7_adc_disable(indio_dev);
>>>   	stm32h7_adc_enter_pwr_down(adc);
>>>   }
>>>   
>>
>> Reviewed-by: Olivier Moysan <olivier.moysan@...s.st.com>
>>
>> Thanks
>> Olivier
>