Re: [PATCH v3 2/4] iio: adc: ad7949: fix spi messages on non 14-bit controllers
From: Jonathan Cameron <jic23@kernel.org>
Date: 2021-07-17 17:21:23
Also in:
linux-iio, lkml
On Tue, 13 Jul 2021 00:34:23 -0400 Liam Beguin [off-list ref] wrote:
From: Liam Beguin <redacted> 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 <redacted>
A small tidy up below that will make this even neater...
quoted hunk ↗ jump to hunk
--- 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);
quoted hunk ↗ jump to hunk
+ 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.
quoted hunk ↗ jump to hunk
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...
quoted hunk ↗ jump to hunk
+ /* 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");