[PATCH 3/3] iio:adc:at91-sama5d2: add support for signed conversion

[Ludovic Desroches]

The at91-sama5d2 ADC controller can achieve unsigned and signed
conversion. For each channel, a signed and an unsigned variant are
created.
We can't set the sign mode for each channel. For that reason, the
controller has to be configured upon conversion requests.

Signed-off-by: Ludovic Desroches <ludovic.desroches@xxxxxxxxx>
---
 drivers/iio/adc/at91-sama5d2_adc.c | 81 +++++++++++++++++++++++++++++++-------
 1 file changed, 67 insertions(+), 14 deletions(-)

diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
index 5bc038f..d4bf73f 100644
--- a/drivers/iio/adc/at91-sama5d2_adc.c
+++ b/drivers/iio/adc/at91-sama5d2_adc.c
@@ -105,8 +105,26 @@
 #define AT91_SAMA5D2_LCCWR	0x38
 /* Overrun Status Register */
 #define AT91_SAMA5D2_OVER	0x3c
+
 /* Extended Mode Register */
 #define AT91_SAMA5D2_EMR	0x40
+/* Sign Mode */
+#define AT91_SAMA5D2_EMR_SIGNMODE(v)		((v) << 25)
+/*
+ * Single-Ended channels: Unsigned conversions.
+ * Differential channels: Signed conversions.
+ */
+#define AT91_SAMA5D2_EMR_SE_UNSG_DF_SIGN	0
+/*
+ * Single-Ended channels: Signed conversions.
+ * Differential channels: Unsigned conversions.
+ */
+#define AT91_SAMA5D2_EMR_SE_SIGN_DF_UNSG	1
+/* All channels: Unsigned conversions */
+#define AT91_SAMA5D2_EMR_ALL_UNSIGNED		2
+/* All channels: Signed conversions */
+#define AT91_SAMA5D2_EMR_ALL_SIGNED		3
+
 /* Compare Window Register */
 #define AT91_SAMA5D2_CWR	0x44
 /* Channel Gain Register */
@@ -140,13 +158,14 @@
 /* Version Register */
 #define AT91_SAMA5D2_VERSION	0xfc
 
-#define AT91_SAMA5D2_CHAN(num, addr)					\
+#define AT91_SAMA5D2_VOLTAGE_CHANNEL(num, addr, sign_mode)		\
 	{								\
 		.type = IIO_VOLTAGE,					\
 		.channel = num,						\
 		.address = addr,					\
+		.extend_name = (sign_mode == 's') ? "signed" : "unsigned",\
 		.scan_type = {						\
-			.sign = 'u',					\
+			.sign = sign_mode,				\
 			.realbits = 12,					\
 		},							\
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
@@ -156,6 +175,12 @@
 		.indexed = 1,						\
 	}
 
+#define AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(num, addr)		\
+	AT91_SAMA5D2_VOLTAGE_CHANNEL(num, addr, 's')
+
+#define AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(num, addr)	\
+	AT91_SAMA5D2_VOLTAGE_CHANNEL(num, addr, 'u')
+
 #define at91_adc_readl(st, reg)		readl_relaxed(st->base + reg)
 #define at91_adc_writel(st, reg, val)	writel_relaxed(val, st->base + reg)
 
@@ -185,18 +210,30 @@ struct at91_adc_state {
 };
 
 static const struct iio_chan_spec at91_adc_channels[] = {
-	AT91_SAMA5D2_CHAN(0, 0x50),
-	AT91_SAMA5D2_CHAN(1, 0x54),
-	AT91_SAMA5D2_CHAN(2, 0x58),
-	AT91_SAMA5D2_CHAN(3, 0x5c),
-	AT91_SAMA5D2_CHAN(4, 0x60),
-	AT91_SAMA5D2_CHAN(5, 0x64),
-	AT91_SAMA5D2_CHAN(6, 0x68),
-	AT91_SAMA5D2_CHAN(7, 0x6c),
-	AT91_SAMA5D2_CHAN(8, 0x70),
-	AT91_SAMA5D2_CHAN(9, 0x74),
-	AT91_SAMA5D2_CHAN(10, 0x78),
-	AT91_SAMA5D2_CHAN(11, 0x7c),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(0, 0x50),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(1, 0x54),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(2, 0x58),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(3, 0x5c),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(4, 0x60),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(5, 0x64),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(6, 0x68),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(7, 0x6c),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(8, 0x70),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(9, 0x74),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(10, 0x78),
+	AT91_SAMA5D2_UNSIGNED_VOLTAGE_CHANNEL(11, 0x7c),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(0, 0x50),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(1, 0x54),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(2, 0x58),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(3, 0x5c),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(4, 0x60),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(5, 0x64),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(6, 0x68),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(7, 0x6c),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(8, 0x70),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(9, 0x74),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(10, 0x78),
+	AT91_SAMA5D2_SIGNED_VOLTAGE_CHANNEL(11, 0x7c),
 };
 
 static unsigned at91_adc_startup_time(unsigned startup_time_min,
@@ -278,6 +315,7 @@ static int at91_adc_read_raw(struct iio_dev *indio_dev,
 			     int *val, int *val2, long mask)
 {
 	struct at91_adc_state *st = iio_priv(indio_dev);
+	u32 emr;
 	int ret;
 
 	switch (mask) {
@@ -286,6 +324,19 @@ static int at91_adc_read_raw(struct iio_dev *indio_dev,
 
 		st->chan = chan;
 
+		/* Read EMR register and clear 'sign mode' field */
+		emr = at91_adc_readl(st, AT91_SAMA5D2_EMR)
+		      & AT91_SAMA5D2_EMR_SIGNMODE(0);
+		/*
+		 * Check if the user requested a conversion on a signed or
+		 * unsigned channel.
+		 */
+		if (chan->scan_type.sign == 's')
+			emr |= AT91_SAMA5D2_EMR_SIGNMODE(AT91_SAMA5D2_EMR_ALL_SIGNED);
+		else
+			emr |= AT91_SAMA5D2_EMR_SIGNMODE(AT91_SAMA5D2_EMR_ALL_UNSIGNED);
+
+		at91_adc_writel(st, AT91_SAMA5D2_EMR, emr);
 		at91_adc_writel(st, AT91_SAMA5D2_CHER, BIT(chan->channel));
 		at91_adc_writel(st, AT91_SAMA5D2_IER, BIT(chan->channel));
 		at91_adc_writel(st, AT91_SAMA5D2_CR, AT91_SAMA5D2_CR_START);
@@ -298,6 +349,8 @@ static int at91_adc_read_raw(struct iio_dev *indio_dev,
 
 		if (ret > 0) {
 			*val = st->conversion_value;
+			if (chan->scan_type.sign == 's')
+				*val = sign_extend32(*val, 11);
 			ret = IIO_VAL_INT;
 			st->conversion_done = false;
 		}
-- 
2.5.0