Patch "iio: adc: ti_am335x_adc: fix fifo overrun recovery" has been added to the 4.10-stable tree

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

iio: adc: ti_am335x_adc: fix fifo overrun recovery

to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iio-adc-ti_am335x_adc-fix-fifo-overrun-recovery.patch
and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Michael Engl <[email protected]>
Date: Tue, 3 Oct 2017 13:57:00 +0100
Subject: iio: adc: ti_am335x_adc: fix fifo overrun recovery

From: Michael Engl <[email protected]>

commit e83bb3e6f3efa21f4a9d883a25d0ecd9dfb431e1 upstream.

The tiadc_irq_h(int irq, void *private) function is handling FIFO overruns by clearing flags, disabling and enabling the ADC to recover.

If the ADC is running in continuous mode a FIFO overrun happens regularly. If the disabling of the ADC happens concurrently with a new conversion. It might happen that the enabling of the ADC is ignored by the hardware. This stops the ADC permanently. No more interrupts are triggered.

According to the AM335x Reference Manual (SPRUH73H October 2011 - Revised April 2013 - Chapter 12.4 and 12.5) it is necessary to check the ADC FSM bits in REG_ADCFSM before enabling the ADC again. Because the disabling of the ADC is done right after the current conversion has been finished.

To trigger this bug it is necessary to run the ADC in continuous mode. The ADC values of all channels need to be read in an endless loop. The bug appears within the first 6 hours (~5.4 million handled FIFO overruns). The user space application will hang on reading new values from the character device.

---
 drivers/iio/adc/ti_am335x_adc.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

@@ -169,7 +169,9 @@ static irqreturn_t tiadc_irq_h(int irq,
 {
 	struct iio_dev *indio_dev = private;
 	struct tiadc_device *adc_dev = iio_priv(indio_dev);
-	unsigned int status, config;
+	unsigned int status, config, adc_fsm;
+	unsigned short count = 0;
+
 	status = tiadc_readl(adc_dev, REG_IRQSTATUS);
 
 	/*

@@ -183,6 +185,15 @@ static irqreturn_t tiadc_irq_h(int irq,
 		tiadc_writel(adc_dev, REG_CTRL, config);
 		tiadc_writel(adc_dev, REG_IRQSTATUS, IRQENB_FIFO1OVRRUN
 				| IRQENB_FIFO1UNDRFLW | IRQENB_FIFO1THRES);
+
+		/* wait for idle state.
+		 * ADC needs to finish the current conversion
+		 * before disabling the module
+		 */
+		do {
+			adc_fsm = tiadc_readl(adc_dev, REG_ADCFSM);
+		} while (adc_fsm != 0x10 && count++ < 100);
+
 		tiadc_writel(adc_dev, REG_CTRL, (config | CNTRLREG_TSCSSENB));
 		return IRQ_HANDLED;
 	} else if (status & IRQENB_FIFO1THRES) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.10/iio-adc-ti_am335x_adc-fix-fifo-overrun-recovery.patch