adc: read error: Device or resource busy

From fa15f2236fdd76f450cc41aee93d5934c23f9706 Mon Sep 17 00:00:00 2001
From: Jeff Lance <j-lance1@ti.com>
Date: Thu, 24 Apr 2014 10:51:16 -0500
Subject: [PATCH] iio: ti_am335x_adc: Fix unecessary restrictions on ADC input
 selection

Franklin Cooper found that there are limitations on the order of
channels you select when setting up the ADC in the device tree bindings.
You must select channel 7 first followed in reverse sequential order:
6 5 4 3 2 1 0.  You can select any number of inputs but they must start
with 7 and count backwards. This bug looks like it may have stemmed from
a documentation issue.  The TRM indicates bits 19-16 of the FIFO1DATA
register report back the channel that captured the data, when actually,
it is the step number. Now if we modify tiadc_read_raw() to compare the
expected step id with the FIFO1DATA register bits 19-16, there are no
longer any restrictions on order when selecting channels in the Device Tree.

Before the fix, if you wanted to select 4 channels, they had to be:
{4 5 6 7}, otherwise you would get (EBUSY) return values on any
channels that did not follow the restriction.  Now any combination of
(0 - 7) will work. Of course it depends on if you are using the
touchscreen and what channels are available for ADC.

Signed-off-by: Jeff Lance <j-lance1@ti.com>
---
 drivers/iio/adc/ti_am335x_adc.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
index 95b43e9..cb991ea 100644
--- a/drivers/iio/adc/ti_am335x_adc.c
+++ b/drivers/iio/adc/ti_am335x_adc.c
@@ -158,7 +158,7 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
 		int *val, int *val2, long mask)
 {
 	struct tiadc_device *adc_dev = iio_priv(indio_dev);
-	int i, map_val;
+	int i;
 	unsigned int fifo1count, read, stepid;
 	u32 step = UINT_MAX;
 	bool found = false;
@@ -179,7 +179,6 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
 			return -EAGAIN;
 		}
 	}
-	map_val = chan->channel + TOTAL_CHANNELS;
 
 	/*
 	 * When the sub-system is first enabled,
@@ -209,7 +208,7 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
 		stepid = read & FIFOREAD_CHNLID_MASK;
 		stepid = stepid >> 0x10;
 
-		if (stepid == map_val) {
+		if (stepid == step) {
 			read = read & FIFOREAD_DATA_MASK;
 			found = true;
 			*val = read;
-- 
1.7.9.5