iio: adc: at91-sama5d2_adc: handle unfinished conversions

It can happen that on IRQ trigger, not all conversions are done if
we are enabling multiple channels.
The IRQ is triggered on first EOC (end of channel), but it can happen
that not all channels are done. This leads into erroneous reports to
userspace (zero values or previous values).
To solve this, in trigger handler, check if the mask of done channels
is the same as the mask of active scan channels.
If it's the same, proceed and push to buffers. Otherwise, use usleep
to sleep until the conversion is done or we timeout.
Normally, it should happen that in a short time fashion, all channels are
ready, since the first IRQ triggered.
If a hardware fault happens (for example the clock suddently dissappears),
the handler will not be completed, in which case we do not report anything to
userspace anymore.
Also, change from using the EOC interrupts to DRDY interrupt.
This helps with the fact that not 'n' interrupt statuses are enabled,
each being able to trigger an interrupt, and instead only data ready
interrupt can wake up the CPU. Like this, when data is ready, check in
handler which and how many channels are done. While the DRDY is raised,
other IRQs cannot occur. Once the channel data is being read, we ack the
IRQ and finish the conversion.

Signed-off-by: Eugen Hristev <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>

Author: ehristev

drivers/iio/adc/at91-sama5d2_adc.c

@@ -8,6 +8,7 @@
 
 #include <linux/bitops.h>
 #include <linux/clk.h>
+#include <linux/delay.h>
 #include <linux/dma-mapping.h>
 #include <linux/dmaengine.h>
 #include <linux/interrupt.h>
@@ -100,6 +101,8 @@
 #define AT91_SAMA5D2_IER_YRDY   BIT(21)
 /* Interrupt Enable Register - TS pressure measurement ready */
 #define AT91_SAMA5D2_IER_PRDY   BIT(22)
+/* Interrupt Enable Register - Data ready */
+#define AT91_SAMA5D2_IER_DRDY   BIT(24)
 /* Interrupt Enable Register - general overrun error */
 #define AT91_SAMA5D2_IER_GOVRE BIT(25)
 /* Interrupt Enable Register - Pen detect */
@@ -486,6 +489,21 @@ static inline int at91_adc_of_xlate(struct iio_dev *indio_dev,
 	return at91_adc_chan_xlate(indio_dev, iiospec->args[0]);
 }
 
+static unsigned int at91_adc_active_scan_mask_to_reg(struct iio_dev *indio_dev)
+{
+	u32 mask = 0;
+	u8 bit;
+
+	for_each_set_bit(bit, indio_dev->active_scan_mask,
+			 indio_dev->num_channels) {
+		struct iio_chan_spec const *chan =
+			 at91_adc_chan_get(indio_dev, bit);
+		mask |= BIT(chan->channel);
+	}
+
+	return mask & GENMASK(11, 0);
+}
+
 static void at91_adc_config_emr(struct at91_adc_state *st)
 {
 	/* configure the extended mode register */
@@ -746,25 +764,23 @@ static int at91_adc_configure_trigger(struct iio_trigger *trig, bool state)
 			at91_adc_writel(st, AT91_SAMA5D2_COR, cor);
 		}
 
-		if (state) {
+		if (state)
 			at91_adc_writel(st, AT91_SAMA5D2_CHER,
 					BIT(chan->channel));
-			/* enable irq only if not using DMA */
-			if (!st->dma_st.dma_chan) {
-				at91_adc_writel(st, AT91_SAMA5D2_IER,
-						BIT(chan->channel));
-			}
-		} else {
-			/* disable irq only if not using DMA */
-			if (!st->dma_st.dma_chan) {
-				at91_adc_writel(st, AT91_SAMA5D2_IDR,
-						BIT(chan->channel));
-			}
+		else
 			at91_adc_writel(st, AT91_SAMA5D2_CHDR,
 					BIT(chan->channel));
-		}
 	}
 
+	/* Nothing to do if using DMA */
+	if (st->dma_st.dma_chan)
+		return 0;
+
+	if (state)
+		at91_adc_writel(st, AT91_SAMA5D2_IER, AT91_SAMA5D2_IER_DRDY);
+	else
+		at91_adc_writel(st, AT91_SAMA5D2_IDR, AT91_SAMA5D2_IER_DRDY);
+
 	return 0;
 }
 
@@ -781,6 +797,7 @@ static int at91_adc_reenable_trigger(struct iio_trigger *trig)
 
 	/* Needed to ACK the DRDY interruption */
 	at91_adc_readl(st, AT91_SAMA5D2_LCDR);
+
 	return 0;
 }
 
@@ -1015,6 +1032,22 @@ static void at91_adc_trigger_handler_nodma(struct iio_dev *indio_dev,
 	int i = 0;
 	int val;
 	u8 bit;
+	u32 mask = at91_adc_active_scan_mask_to_reg(indio_dev);
+	unsigned int timeout = 50;
+
+	/*
+	 * Check if the conversion is ready. If not, wait a little bit, and
+	 * in case of timeout exit with an error.
+	 */
+	while ((at91_adc_readl(st, AT91_SAMA5D2_ISR) & mask) != mask &&
+	       timeout) {
+		usleep_range(50, 100);
+		timeout--;
+	}
+
+	/* Cannot read data, not ready. Continue without reporting data */
+	if (!timeout)
+		return;
 
 	for_each_set_bit(bit, indio_dev->active_scan_mask,
 			 indio_dev->num_channels) {
@@ -1281,7 +1314,8 @@ static irqreturn_t at91_adc_interrupt(int irq, void *private)
 		status = at91_adc_readl(st, AT91_SAMA5D2_XPOSR);
 		status = at91_adc_readl(st, AT91_SAMA5D2_YPOSR);
 		status = at91_adc_readl(st, AT91_SAMA5D2_PRESSR);
-	} else if (iio_buffer_enabled(indio) && !st->dma_st.dma_chan) {
+	} else if (iio_buffer_enabled(indio) &&
+		   (status & AT91_SAMA5D2_IER_DRDY)) {
 		/* triggered buffer without DMA */
 		disable_irq_nosync(irq);
 		iio_trigger_poll(indio->trig);