[PATCH 1/1] iio: imx8qxp-adc: fix irq flood when call imx8qxp_adc_read_raw()

[Frank Li]

> -----Original Message-----
> From: Bough Chen <haibo.chen at nxp.com>
> Sent: Wednesday, November 30, 2022 3:58 AM
> To: Frank Li <frank.li at nxp.com>; Cai Huoqing <cai.huoqing at linux.dev>;
> Jonathan Cameron <jic23 at kernel.org>; Lars-Peter Clausen
> <lars at metafoo.de>; Shawn Guo <shawnguo at kernel.org>; Sascha Hauer
> <s.hauer at pengutronix.de>; Pengutronix Kernel Team
> <kernel at pengutronix.de>; Fabio Estevam <festevam at gmail.com>; dl-linux-
> imx <linux-imx at nxp.com>; open list:NXP i.MX 8QXP ADC DRIVER <linux-
> iio at vger.kernel.org>; moderated list:ARM/FREESCALE IMX / MXC ARM
> ARCHITECTURE <linux-arm-kernel at lists.infradead.org>; open list <linux-
> kernel at vger.kernel.org>
> Cc: imx at lists.linux.dev
> Subject: RE: [PATCH 1/1] iio: imx8qxp-adc: fix irq flood when call
> imx8qxp_adc_read_raw()
> 
> > -----Original Message-----
> > From: Frank Li <frank.li at nxp.com>
> > Sent: 2022年11月30日 0:46
> > To: Cai Huoqing <cai.huoqing at linux.dev>; Bough Chen
> <haibo.chen at nxp.com>;
> > Jonathan Cameron <jic23 at kernel.org>; Lars-Peter Clausen
> <lars at metafoo.de>;
> > Shawn Guo <shawnguo at kernel.org>; Sascha Hauer
> <s.hauer at pengutronix.de>;
> > Pengutronix Kernel Team <kernel at pengutronix.de>; Fabio Estevam
> > <festevam at gmail.com>; dl-linux-imx <linux-imx at nxp.com>; open list:NXP
> i.MX
> > 8QXP ADC DRIVER <linux-iio at vger.kernel.org>; moderated
> > list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE
> > <linux-arm-kernel at lists.infradead.org>; open list <linux-
> kernel at vger.kernel.org>
> > Cc: imx at lists.linux.dev
> > Subject: [PATCH 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 at vger.kernel.org
> >
> > Signed-off-by: Frank Li <Frank.Li at nxp.com>
> > ---
> >  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..3cfba5c0fa34 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;
> > @@ -265,6 +267,7 @@ 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));
> @@
> > -272,6 +275,10 @@ static irqreturn_t imx8qxp_adc_isr(int irq, void *dev_id)
> >  	if (fifo_count)
> >  		complete(&adc->completion);
> >
> > +	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));
> 
> Hi Frank,
> 
> Since the ADC mode is config as single-ended 12-bit conversion, every time
> when trigger the ADC conversion, only one 12-bit data push into fifo.
> And we also config the fifo watermark as 1. So here only need to read once. I
> already confirmed on my board.

Interrupt handle should guarantee read all data from FIFO.  If somewhere increase
Watermark or set auto continue sample,  irq flood will be happen again.

Best regards
Frank Li 

> 
> Best Regards
> Haibo Chen
> > +
> >  	return IRQ_HANDLED;
> >  }
> >
> > --
> > 2.34.1