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

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Date:   Thu, 28 Oct 2021 15:19:21 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Fabrice Gasnier <fabrice.gasnier@...s.st.com>
Cc:     Olivier MOYSAN <olivier.moysan@...s.st.com>,
        <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 Mon, 25 Oct 2021 09:43:10 +0200
Fabrice Gasnier <fabrice.gasnier@...s.st.com> wrote:

> 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.

Added the word current to the title which I think makes it clear.
> 
> >   
> >> 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.

Applied to the fixes-togreg branch of iio.git, targeting a pull request
some time shortly after rc1.

Thanks,

Jonathan

> 
> 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  
> >