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Date: Sat, 17 Jul 2021 18:23:26 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Liam Beguin <liambeguin@...il.com>
Cc: lars@...afoo.de, Michael.Hennerich@...log.com,
charles-antoine.couret@...ensium.com, Nuno.Sa@...log.com,
linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
devicetree@...r.kernel.org, robh+dt@...nel.org
Subject: Re: [PATCH v3 2/4] iio: adc: ad7949: fix spi messages on non 14-bit
controllers
On Tue, 13 Jul 2021 00:34:23 -0400
Liam Beguin <liambeguin@...il.com> wrote:
> From: Liam Beguin <lvb@...hos.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@...hos.com>
A small tidy up below that will make this even neater...
> ---
> drivers/iio/adc/ad7949.c | 68 +++++++++++++++++++++++++++++++++++-----
> 1 file changed, 60 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> index 0b549b8bd7a9..65f78751225b 100644
> --- a/drivers/iio/adc/ad7949.c
> +++ b/drivers/iio/adc/ad7949.c
> @@ -12,6 +12,7 @@
> #include <linux/regulator/consumer.h>
> #include <linux/spi/spi.h>
> #include <linux/bitfield.h>
> +#include <asm/unaligned.h>
>
> #define AD7949_MASK_TOTAL GENMASK(13, 0)
>
> @@ -67,6 +68,7 @@ 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
> @@ -77,6 +79,7 @@ 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;
> @@ -86,19 +89,37 @@ 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;
> + u8 buf8[2];
> 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 */
> + buf8[0] = FIELD_GET(GENMASK(13, 6), ad7949_adc->cfg);
> + buf8[1] = FIELD_GET(GENMASK(5, 0), ad7949_adc->cfg) << 2;
> + memcpy(&ad7949_adc->buffer, buf8, 2);
Can probably tidy this up given the form - all we actually need to do is ensure the
value ends up big endian.
/* Type is only big endian for this case as must be done as two transfers */
ad7949_adc->buffer = (u16)cpu_to_be16(ad7959_adc->cfg << 2);
> + break;
> + default:
> + dev_err(&ad7949_adc->indio_dev->dev, "unsupported BPW\n");
> + return -EINVAL;
> + }
> +
> spi_message_init_with_transfers(&msg, tx, 1);
> ret = spi_sync(ad7949_adc->spi, &msg);
>
> @@ -115,14 +136,13 @@ 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);
> + u8 buf8[2];
As below, not needed that I can see.
> 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,
> },
> };
>
> @@ -157,7 +177,26 @@ 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 */
> + *val >>= 16 - ad7949_adc->resolution;
> + break;
> + case 14:
> + *val = ad7949_adc->buffer & GENMASK(13, 0);
> + break;
> + case 8:
> + memcpy(buf8, &ad7949_adc->buffer, 2);
> + /* Convert byte array to u16, MSB first */
> + *val = get_unaligned_be16(buf8);
Why the local copy first?
*val = get_unaligned_be16(ad7949_adc->buffer);
should get what you want, it doesn't care about the type.
Even better, that buffer is aligned, so we can do
be16_to_cpu() safely I think...
> + /* Shift-out padding bits */
> + *val >>= 16 - ad7949_adc->resolution;
> + break;
> + default:
> + dev_err(&ad7949_adc->indio_dev->dev, "unsupported BPW\n");
> + return -EINVAL;
> + }
>
> return 0;
> }
> @@ -265,6 +304,7 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
>
> static int ad7949_spi_probe(struct spi_device *spi)
> {
> + u32 spi_ctrl_mask = spi->controller->bits_per_word_mask;
> struct device *dev = &spi->dev;
> const struct ad7949_adc_spec *spec;
> struct ad7949_adc_chip *ad7949_adc;
> @@ -291,6 +331,18 @@ static int ad7949_spi_probe(struct spi_device *spi)
> indio_dev->num_channels = spec->num_channels;
> ad7949_adc->resolution = spec->resolution;
>
> + /* Set SPI bits per word */
> + if (spi_ctrl_mask & SPI_BPW_MASK(ad7949_adc->resolution)) {
> + ad7949_adc->bits_per_word = ad7949_adc->resolution;
> + } else if (spi_ctrl_mask == SPI_BPW_MASK(16)) {
> + ad7949_adc->bits_per_word = 16;
> + } else if (spi_ctrl_mask == SPI_BPW_MASK(8)) {
> + ad7949_adc->bits_per_word = 8;
> + } else {
> + dev_err(dev, "unable to find common BPW with spi controller\n");
> + return -EINVAL;
> + }
> +
> ad7949_adc->vref = devm_regulator_get(dev, "vref");
> if (IS_ERR(ad7949_adc->vref)) {
> dev_err(dev, "fail to request regulator\n");
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