[PATCH v1 1/3] iio: adc: ad_sigma_delta: Add CS assert function

[Alisa-Dariana Roman <alisadariana@xxxxxxxxx>]

Some sigma-delta ADCs, such as AD7191 and AD7780, have no registers and
start conversion when CS is asserted. Add helper function to support
this use case by allowing devices to assert CS without performing
register operations.

This function can be used by drivers through their set_mode callback.

Signed-off-by: Alisa-Dariana Roman <alisa.roman@xxxxxxxxxx>
---
 drivers/iio/adc/ad_sigma_delta.c       | 24 ++++++++++++++++++++++++
 include/linux/iio/adc/ad_sigma_delta.h |  1 +
 2 files changed, 25 insertions(+)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index 0f355dac7813..c0f33d4baddf 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -48,6 +48,30 @@ void ad_sd_set_comm(struct ad_sigma_delta *sigma_delta, uint8_t comm)
 }
 EXPORT_SYMBOL_NS_GPL(ad_sd_set_comm, "IIO_AD_SIGMA_DELTA");
 
+/**
+ * ad_sd_assert_cs() - Assert chip select line
+ *
+ * @sigma_delta: The sigma delta device
+ *
+ * Returns 0 on success, an error code otherwise.
+ **/
+int ad_sd_assert_cs(struct ad_sigma_delta *sigma_delta)
+{
+	struct spi_transfer t = {
+		.len = 0,
+		.cs_change = sigma_delta->keep_cs_asserted,
+	};
+	struct spi_message m;
+
+	spi_message_init(&m);
+	spi_message_add_tail(&t, &m);
+
+	if (sigma_delta->bus_locked)
+		return spi_sync_locked(sigma_delta->spi, &m);
+	return spi_sync(sigma_delta->spi, &m);
+}
+EXPORT_SYMBOL_NS_GPL(ad_sd_assert_cs, IIO_AD_SIGMA_DELTA);
+
 /**
  * ad_sd_write_reg() - Write a register
  *
diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
index 417073c52380..99ab56d04793 100644
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -178,6 +178,7 @@ static inline int ad_sigma_delta_postprocess_sample(struct ad_sigma_delta *sd,
 }
 
 void ad_sd_set_comm(struct ad_sigma_delta *sigma_delta, uint8_t comm);
+int ad_sd_assert_cs(struct ad_sigma_delta *sigma_delta);
 int ad_sd_write_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
 	unsigned int size, unsigned int val);
 int ad_sd_read_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
-- 
2.43.0