[PATCH v1 2/4] iio: adc: ad7949: fix spi messages on non 14-bit controllers

Liam Beguin
2021-07-08T23:56:49Z

From: Liam Beguin <lvb@xiphos.com>

This driver supports devices with 14-bit and 16-bit sample sizes.
This is not always handled properly by spi controllers and can fail. To
work around this limitation, pad samples to 16-bit and split the sample
into two 8-bit messages in the event that only 8-bit messages are
supported by the controller.

Signed-off-by: Liam Beguin <lvb@xiphos.com>
---
drivers/iio/adc/ad7949.c | 67 ++++++++++++++++++++++++++++++++++------
1 file changed, 58 insertions(+), 9 deletions(-)

diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
index 93aacf4f680b..bbc6b56330a3 100644
--- a/drivers/iio/adc/ad7949.c
+++ b/drivers/iio/adc/ad7949.c
@@ -11,6 +11,7 @@
#include <linux/module.h>
#include <linux/regulator/consumer.h>
#include <linux/spi/spi.h>
+#include <linux/bitfield.h>

#define AD7949_MASK_TOTAL GENMASK(13, 0)
#define AD7949_CFG_REG_SIZE_BITS 14
@@ -57,6 +58,7 @@ static const struct ad7949_adc_spec ad7949_adc_spec[] = {
* @indio_dev: reference to iio structure
* @spi: reference to spi structure
* @resolution: resolution of the chip
+ * @bits_per_word: number of bits per SPI word
* @cfg: copy of the configuration register
* @current_channel: current channel in use
* @buffer: buffer to send / receive data to / from device
@@ -67,28 +69,59 @@ struct ad7949_adc_chip {
struct iio_dev *indio_dev;
struct spi_device *spi;
u8 resolution;
+ u8 bits_per_word;
u16 cfg;
unsigned int current_channel;
- u16 buffer ____cacheline_aligned;
+ union {
+ __be16 buffer;
+ u8 buf8[2];
+ } ____cacheline_aligned;
};

+static void ad7949_set_bits_per_word(struct ad7949_adc_chip *ad7949_adc)
+{
+ u32 adc_mask = SPI_BPW_MASK(ad7949_adc->resolution);
+ u32 bpw = adc_mask & ad7949_adc->spi->controller->bits_per_word_mask;
+
+ if (bpw == adc_mask)
+ ad7949_adc->bits_per_word = ad7949_adc->resolution;
+ else if (bpw == SPI_BPW_MASK(16))
+ ad7949_adc->bits_per_word = 16;
+ else
+ ad7949_adc->bits_per_word = 8;
+}
+
static int ad7949_spi_write_cfg(struct ad7949_adc_chip *ad7949_adc, u16 val,
u16 mask)
{
int ret;
- int bits_per_word = ad7949_adc->resolution;
- int shift = bits_per_word - AD7949_CFG_REG_SIZE_BITS;
struct spi_message msg;
struct spi_transfer tx[] = {
{
.tx_buf = &ad7949_adc->buffer,
.len = 2,
- .bits_per_word = bits_per_word,
+ .bits_per_word = ad7949_adc->bits_per_word,
},
};

+ ad7949_adc->buffer = 0;
ad7949_adc->cfg = (val & mask) | (ad7949_adc->cfg & ~mask);
- ad7949_adc->buffer = ad7949_adc->cfg << shift;
+
+ switch (ad7949_adc->bits_per_word) {
+ case 16:
+ ad7949_adc->buffer = ad7949_adc->cfg << 2;
+ break;
+ case 14:
+ ad7949_adc->buffer = ad7949_adc->cfg;
+ break;
+ case 8:
+ /* Pack 14-bit value into 2 bytes, MSB first */
+ ad7949_adc->buf8[0] = FIELD_GET(GENMASK(13, 6), ad7949_adc->cfg);
+ ad7949_adc->buf8[1] = FIELD_GET(GENMASK(5, 0), ad7949_adc->cfg);
+ ad7949_adc->buf8[1] = ad7949_adc->buf8[1] << 2;
+ break;
+ }
+
spi_message_init_with_transfers(&msg, tx, 1);
ret = spi_sync(ad7949_adc->spi, &msg);

@@ -105,14 +138,12 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,
{
int ret;
int i;
- int bits_per_word = ad7949_adc->resolution;
- int mask = GENMASK(ad7949_adc->resolution - 1, 0);
struct spi_message msg;
struct spi_transfer tx[] = {
{
.rx_buf = &ad7949_adc->buffer,
.len = 2,
- .bits_per_word = bits_per_word,
+ .bits_per_word = ad7949_adc->bits_per_word,
},
};

@@ -147,7 +178,24 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,

ad7949_adc->current_channel = channel;

- *val = ad7949_adc->buffer & mask;
+ switch (ad7949_adc->bits_per_word) {
+ case 16:
+ *val = ad7949_adc->buffer;
+ /* Shift-out padding bits */
+ if (ad7949_adc->resolution == 14)
+ *val = *val >> 2;
+ break;
+ case 14:
+ *val = ad7949_adc->buffer & GENMASK(13, 0);
+ break;
+ case 8:
+ /* Convert byte array to u16, MSB first */
+ *val = (ad7949_adc->buf8[0] << 8) | ad7949_adc->buf8[1];
+ /* Shift-out padding bits */
+ if (ad7949_adc->resolution == 14)
+ *val = *val >> 2;
+ break;
+ }

return 0;
}
@@ -280,6 +328,7 @@ static int ad7949_spi_probe(struct spi_device *spi)
spec = &ad7949_adc_spec[spi_get_device_id(spi)->driver_data];
indio_dev->num_channels = spec->num_channels;
ad7949_adc->resolution = spec->resolution;
+ ad7949_set_bits_per_word(ad7949_adc);

ad7949_adc->vref = devm_regulator_get(dev, "vref");
if (IS_ERR(ad7949_adc->vref)) {
--
2.30.1.489.g328c10930387