[PATCH 4.4 33/47] iio: ad_sigma_delta: Implement a dedicated reset function

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dragos Bogdan <dragos.bogdan@xxxxxxxxxx>

commit 7fc10de8d49a748c476532c9d8e8fe19e548dd67 upstream.

Since most of the SD ADCs have the option of reseting the serial
interface by sending a number of SCLKs with CS = 0 and DIN = 1,
a dedicated function that can do this is usefull.

Needed for the patch:  iio: ad7793: Fix the serial interface reset
Signed-off-by: Dragos Bogdan <dragos.bogdan@xxxxxxxxxx>
Acked-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iio/adc/ad_sigma_delta.c       |   28 ++++++++++++++++++++++++++++
 include/linux/iio/adc/ad_sigma_delta.h |    3 +++
 2 files changed, 31 insertions(+)

--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -177,6 +177,34 @@ out:
 }
 EXPORT_SYMBOL_GPL(ad_sd_read_reg);
 
+/**
+ * ad_sd_reset() - Reset the serial interface
+ *
+ * @sigma_delta: The sigma delta device
+ * @reset_length: Number of SCLKs with DIN = 1
+ *
+ * Returns 0 on success, an error code otherwise.
+ **/
+int ad_sd_reset(struct ad_sigma_delta *sigma_delta,
+	unsigned int reset_length)
+{
+	uint8_t *buf;
+	unsigned int size;
+	int ret;
+
+	size = DIV_ROUND_UP(reset_length, 8);
+	buf = kcalloc(size, sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	memset(buf, 0xff, size);
+	ret = spi_write(sigma_delta->spi, buf, size);
+	kfree(buf);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ad_sd_reset);
+
 static int ad_sd_calibrate(struct ad_sigma_delta *sigma_delta,
 	unsigned int mode, unsigned int channel)
 {
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -111,6 +111,9 @@ int ad_sd_write_reg(struct ad_sigma_delt
 int ad_sd_read_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
 	unsigned int size, unsigned int *val);
 
+int ad_sd_reset(struct ad_sigma_delta *sigma_delta,
+	unsigned int reset_length);
+
 int ad_sigma_delta_single_conversion(struct iio_dev *indio_dev,
 	const struct iio_chan_spec *chan, int *val);
 int ad_sd_calibrate_all(struct ad_sigma_delta *sigma_delta,