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

Sa, Nuno
2021-07-09T08:20:06Z

> -----Original Message-----
> From: Liam Beguin <liambeguin@gmail.com>
> Sent: Friday, July 9, 2021 1:56 AM
> To: liambeguin@gmail.com; lars@metafoo.de; Hennerich, Michael
> <Michael.Hennerich@analog.com>; jic23@kernel.org; charles-
> antoine.couret@essensium.com
> Cc: linux-kernel@vger.kernel.org; linux-iio@vger.kernel.org;
> devicetree@vger.kernel.org; robh+dt@kernel.org
> Subject: [PATCH v1 2/4] iio: adc: ad7949: fix spi messages on non 14-bit
> controllers
>
> [External]
>
> 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;
> + }

Honestly I didn't went through the driver but just a question... Are we
sure that 'ad7949_adc->resolution' will have something valid (8, 14, 16)?
A default statement is always a nice to have :).

> 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