patch "iio: imx8qxp-adc: fix irq flood when call imx8qxp_adc_read_raw()" added to char-misc-linus

This is a note to let you know that I've just added the patch titled

iio: imx8qxp-adc: fix irq flood when call imx8qxp_adc_read_raw()

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 0fc3562a993c3dc41d1177b3983d9300d0db1d4d Mon Sep 17 00:00:00 2001
From: Frank Li <[email protected]>
Date: Thu, 1 Dec 2022 09:01:10 -0500
Subject: 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.

---
 drivers/iio/adc/imx8qxp-adc.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

index 36777b827165..f5a0fc9e64c5 100644
@@ -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);
 

2.39.1