linux-kernel - RE: [PATCH v2 1/1] iio: imx8qxp-adc: fix irq flood when call imx8qxp_adc_read

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Date:   Fri, 2 Dec 2022 03:23:55 +0000
From:   Bough Chen <haibo.chen@....com>
To:     Frank Li <frank.li@....com>
CC:     "cai.huoqing@...ux.dev" <cai.huoqing@...ux.dev>,
        "festevam@...il.com" <festevam@...il.com>,
        "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>
Subject: RE: [PATCH v2 1/1] iio: imx8qxp-adc: fix irq flood when call
 imx8qxp_adc_read_raw()

> -----Original Message-----
> From: Frank Li <frank.li@....com>
> Sent: 2022年12月1日 22:01
> To: Bough Chen <haibo.chen@....com>
> Cc: cai.huoqing@...ux.dev; festevam@...il.com; Frank Li <frank.li@....com>;
> imx@...ts.linux.dev; jic23@...nel.org; kernel@...gutronix.de;
> lars@...afoo.de; linux-arm-kernel@...ts.infradead.org;
> linux-iio@...r.kernel.org; dl-linux-imx <linux-imx@....com>;
> linux-kernel@...r.kernel.org; s.hauer@...gutronix.de; shawnguo@...nel.org
> Subject: [PATCH v2 1/1] iio: imx8qxp-adc: fix irq flood when call
> imx8qxp_adc_read_raw()
> 
> irq flood happen when run
>     cat /sys/bus/iio/devices/iio:device0/in_voltage1_raw
> 
> imx8qxp_adc_read_raw()
> {
> 	...
> 	enable irq
> 	/* adc start */
> 	writel(1, adc->regs + IMX8QXP_ADR_ADC_SWTRIG);
> 	^^^^ trigger irq flood.
> 	wait_for_completion_interruptible_timeout();
> 	readl(adc->regs + IMX8QXP_ADR_ADC_RESFIFO);
> 	^^^^ clear irq here.
> 	...
> }
> 
> There is only FIFO watermark interrupt at this ADC controller.
> IRQ line will be assert until software read data from FIFO.
> So IRQ flood happen during wait_for_completion_interruptible_timeout().
> 
> Move FIFO read into irq handle to avoid irq flood.
> 
> Fixes: 1e23dcaa1a9f ("iio: imx8qxp-adc: Add driver support for NXP IMX8QXP
> ADC")
> Cc: stable@...r.kernel.org
> 
> Signed-off-by: Frank Li <Frank.Li@....com>

Thanks for the quick fix. The total read count in irq handler is fifo_count which is read from register, this is reasonable.

Reviewed-by: Haibo Chen <haibo.chen@....com>

Best Regards
Haibo Chen
> ---
> Change from v1 to v2
>  - move complete() after read fifo
> 
> 
>  drivers/iio/adc/imx8qxp-adc.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/imx8qxp-adc.c b/drivers/iio/adc/imx8qxp-adc.c index
> 36777b827165..f5a0fc9e64c5 100644
> --- a/drivers/iio/adc/imx8qxp-adc.c
> +++ b/drivers/iio/adc/imx8qxp-adc.c
> @@ -86,6 +86,8 @@
> 
>  #define IMX8QXP_ADC_TIMEOUT		msecs_to_jiffies(100)
> 
> +#define IMX8QXP_ADC_MAX_FIFO_SIZE		16
> +
>  struct imx8qxp_adc {
>  	struct device *dev;
>  	void __iomem *regs;
> @@ -95,6 +97,7 @@ struct imx8qxp_adc {
>  	/* Serialise ADC channel reads */
>  	struct mutex lock;
>  	struct completion completion;
> +	u32 fifo[IMX8QXP_ADC_MAX_FIFO_SIZE];
>  };
> 
>  #define IMX8QXP_ADC_CHAN(_idx) {				\
> @@ -238,8 +241,7 @@ static int imx8qxp_adc_read_raw(struct iio_dev
> *indio_dev,
>  			return ret;
>  		}
> 
> -		*val = FIELD_GET(IMX8QXP_ADC_RESFIFO_VAL_MASK,
> -				 readl(adc->regs + IMX8QXP_ADR_ADC_RESFIFO));
> +		*val = adc->fifo[0];
> 
>  		mutex_unlock(&adc->lock);
>  		return IIO_VAL_INT;
> @@ -265,10 +267,15 @@ static irqreturn_t imx8qxp_adc_isr(int irq, void
> *dev_id)  {
>  	struct imx8qxp_adc *adc = dev_id;
>  	u32 fifo_count;
> +	int i;
> 
>  	fifo_count = FIELD_GET(IMX8QXP_ADC_FCTRL_FCOUNT_MASK,
>  			       readl(adc->regs + IMX8QXP_ADR_ADC_FCTRL));
> 
> +	for (i = 0; i < fifo_count; i++)
> +		adc->fifo[i] = FIELD_GET(IMX8QXP_ADC_RESFIFO_VAL_MASK,
> +				readl_relaxed(adc->regs + IMX8QXP_ADR_ADC_RESFIFO));
> +
>  	if (fifo_count)
>  		complete(&adc->completion);
> 
> --
> 2.34.1