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

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Message-ID: <77f3593a-0e94-f5ab-f102-86ba8d0f1a3b@foss.st.com>
Date:   Fri, 22 Oct 2021 14:38:52 +0200
From:   Olivier MOYSAN <olivier.moysan@...s.st.com>
To:     Fabrice Gasnier <fabrice.gasnier@...s.st.com>, <jic23@...nel.org>
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

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")
> 
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...s.st.com>
> ---
>   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