[PATCH v2 1/2] iio/adc: ingenic: Fix channel offsets in buffer

[Artur Rojek]

Consumers expect the buffer to only contain enabled channels. While
preparing the buffer, the driver makes two mistakes:
1) It inserts empty data for disabled channels.
2) Each ADC readout contains samples for two 16-bit channels. If either
   of them is active, the whole 32-bit sample is pushed into the buffer
   as-is.

Both of those issues cause the active channels to appear at the wrong
offsets in the buffer. Fix the above by demuxing samples for active
channels only.

This has remained unnoticed, as all the consumers so far were only using
channels 0 and 1, leaving them unaffected by changes introduced in this
commit.

Signed-off-by: Artur Rojek <contact@xxxxxxxxxxxxxx>
Tested-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
---

v2: - demux active channels from ADC readouts 
    - clarify in the commit description that this patch doesn't impact
      existing consumers of this driver

 drivers/iio/adc/ingenic-adc.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/adc/ingenic-adc.c b/drivers/iio/adc/ingenic-adc.c
index a7325dbbb99a..093710a7ad4c 100644
--- a/drivers/iio/adc/ingenic-adc.c
+++ b/drivers/iio/adc/ingenic-adc.c
@@ -802,13 +802,19 @@ static irqreturn_t ingenic_adc_irq(int irq, void *data)
 	struct ingenic_adc *adc = iio_priv(iio_dev);
 	unsigned long mask = iio_dev->active_scan_mask[0];
 	unsigned int i;
-	u32 tdat[3];
-
-	for (i = 0; i < ARRAY_SIZE(tdat); mask >>= 2, i++) {
-		if (mask & 0x3)
-			tdat[i] = readl(adc->base + JZ_ADC_REG_ADTCH);
-		else
-			tdat[i] = 0;
+	u16 tdat[6];
+	u32 val;
+
+	memset(tdat, 0, ARRAY_SIZE(tdat));
+	for (i = 0; mask && i < ARRAY_SIZE(tdat); mask >>= 2) {
+		if (mask & 0x3) {
+			val = readl(adc->base + JZ_ADC_REG_ADTCH);
+			/* Two channels per sample. Demux active. */
+			if (mask & BIT(0))
+				tdat[i++] = val & 0xffff;
+			if (mask & BIT(1))
+				tdat[i++] = val >> 16;
+		}
 	}
 
 	iio_push_to_buffers(iio_dev, tdat);
-- 
2.40.1