linux-kernel - Re: [PATCH 2/2] iio: adc: stm32: Fix check for spurious IRQs on STM32F4

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Message-ID: <32a7849b-c631-f80d-b29c-2a790ac641ec@foss.st.com>
Date:   Fri, 13 May 2022 15:13:53 +0200
From:   Fabrice Gasnier <fabrice.gasnier@...s.st.com>
To:     Yannick Brosseau <yannick.brosseau@...il.com>, <jic23@...nel.org>,
        <lars@...afoo.de>, <mcoquelin.stm32@...il.com>,
        <alexandre.torgue@...s.st.com>, <olivier.moysan@...s.st.com>
CC:     <paul@...pouillou.net>, <linux-iio@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] iio: adc: stm32: Fix check for spurious IRQs on
 STM32F4

On 5/7/22 00:56, Yannick Brosseau wrote:
> The check for spurious IRQs introduced in 695e2f5c289bb assumed that the bits
> in the control and status registers are aligned. This is true for the H7 and MP1
> version, but not the F4.
> 
> Instead of comparing both registers bitwise, we check the bit in the status and control
> for each interrupt we are interested in.
> 

Hi Yannick,

I propose a different approach, see here after.

Same as for patch one,
Fixes: 695e2f5c289b ("iio: adc: stm32-adc: fix a regression when using
dma and irq")

> Signed-off-by: Yannick Brosseau <yannick.brosseau@...il.com>
> ---
>  drivers/iio/adc/stm32-adc.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> index a68ecbda6480..5b0f138333ee 100644
> --- a/drivers/iio/adc/stm32-adc.c
> +++ b/drivers/iio/adc/stm32-adc.c
> @@ -1422,9 +1422,10 @@ static irqreturn_t stm32_adc_threaded_isr(int irq, void *data)
>  		return IRQ_HANDLED;
>  	}
>  
> -	if (!(status & mask))
> +	if(!((status & regs->isr_eoc.mask) && (mask & regs->ier_eoc.mask)) ||
> +           ((status & regs->isr_ovr.mask) && (mask & regs->ier_ovr.mask)))
>  		dev_err_ratelimited(&indio_dev->dev,
> -				    "Unexpected IRQ: IER=0x%08x, ISR=0x%08x\n",
> +				    "Unexpected IRQ: CR1/IER=0x%08x, SR/ISR=0x%08x\n",
>  				    mask, status);


Here, a slightly different approach could be used... There's a long
pending discussion, where Olivier or I should push further patches to
support threadirqs (hopefully soon).
In this discussion with Jonathan [1], he exposed the need to remove this
message. Words from Jonathan:
"This seems 'unusual'.  If this is a spurious interrupt we should be
returning IRQ_NONE and letting the spurious interrupt protection
stuff kick in."

[1]
https://lore.kernel.org/linux-arm-kernel/20210116175333.4d8684c5@archlinux/

So basically, I suggest to completely get rid of this message:

-	if (!(status & mask))
-		dev_err_ratelimited(&indio_dev->dev,
-				    "Unexpected IRQ: IER=0x%08x, ISR=0x%08x\n",
-				    mask, status);

>  
>  	return IRQ_NONE;
> @@ -1438,7 +1439,9 @@ static irqreturn_t stm32_adc_isr(int irq, void *data)
>  	u32 status = stm32_adc_readl(adc, regs->isr_eoc.reg);
>  	u32 mask = stm32_adc_readl(adc, regs->ier_eoc.reg);
>  
> -	if (!(status & mask))
> +	/* Check that we have the interrupt we care about are enabled and active */
> +        if(!((status & regs->isr_eoc.mask) && (mask & regs->ier_eoc.mask)) ||
> +           ((status & regs->isr_ovr.mask) && (mask & regs->ier_ovr.mask)))
>  		return IRQ_WAKE_THREAD;

Here the statement becomes useless, so it could be removed:
-	u32 mask = stm32_adc_readl(adc, regs->ier_eoc.reg);
-
-	if (!(status & mask))
-		return IRQ_WAKE_THREAD;

This would avoid some complexity here (and so headaches or regressions
like the one you've hit).

This also should serve the two purposes:
- fall into kernel generic handler for spurious IRQs (by returning
IRQ_NONE below)
- by the way fix current issue in stm32f4


I Hope this is still inline with Jonathan's words earlier ;-)

Best Regards,
Fabrice

>  
>  	if (status & regs->isr_ovr.mask) {