diff options
Diffstat (limited to 'drivers/iio/adc/ad7949.c')
| -rw-r--r-- | drivers/iio/adc/ad7949.c | 22 |
1 files changed, 17 insertions, 5 deletions
diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c index 5c2b3446fa4a..2c6f60edb7ce 100644 --- a/drivers/iio/adc/ad7949.c +++ b/drivers/iio/adc/ad7949.c @@ -89,6 +89,7 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val, unsigned int channel) { int ret; + int i; int bits_per_word = ad7949_adc->resolution; int mask = GENMASK(ad7949_adc->resolution, 0); struct spi_message msg; @@ -100,12 +101,23 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val, }, }; - ret = ad7949_spi_write_cfg(ad7949_adc, - channel << AD7949_OFFSET_CHANNEL_SEL, - AD7949_MASK_CHANNEL_SEL); - if (ret) - return ret; + /* + * 1: write CFG for sample N and read old data (sample N-2) + * 2: if CFG was not changed since sample N-1 then we'll get good data + * at the next xfer, so we bail out now, otherwise we write something + * and we read garbage (sample N-1 configuration). + */ + for (i = 0; i < 2; i++) { + ret = ad7949_spi_write_cfg(ad7949_adc, + channel << AD7949_OFFSET_CHANNEL_SEL, + AD7949_MASK_CHANNEL_SEL); + if (ret) + return ret; + if (channel == ad7949_adc->current_channel) + break; + } + /* 3: write something and read actual data */ ad7949_adc->buffer = 0; spi_message_init_with_transfers(&msg, tx, 1); ret = spi_sync(ad7949_adc->spi, &msg); |