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

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Date:   Tue, 29 Nov 2022 11:45:29 -0500
From:   Frank Li <Frank.Li@....com>
To:     Cai Huoqing <cai.huoqing@...ux.dev>,
        Haibo Chen <haibo.chen@....com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-iio@...r.kernel.org (open list:NXP i.MX 8QXP ADC DRIVER),
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM/FREESCALE IMX
        / MXC ARM ARCHITECTURE), linux-kernel@...r.kernel.org (open list)
Cc:     imx@...ts.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@...r.kernel.org

Signed-off-by: Frank Li <Frank.Li@....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));
+
 	return IRQ_HANDLED;
 }
 
-- 
2.34.1