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Date: Sun, 29 Aug 2021 12:43:12 -0400
From: Liam Beguin <liambeguin@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
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 v6 2/5] iio: adc: ad7949: fix spi messages on non 14-bit
controllers
On Sun, Aug 29, 2021 at 03:33:34PM +0100, Jonathan Cameron wrote:
> On Sun, 15 Aug 2021 17:33:06 -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 implies different SPI transfer lengths which are not always handled
> > properly by some SPI controllers.
> >
> > To work around this limitation, define a big endian buffer used to split
> > the buffer into two 8-bit messages in the event that the controller
> > doesn't support 14-bit or 16-bit transfers.
> > A separate buffer is introduced here to avoid performing operations on
> > types of different endianness.
> >
> > Since all transfers use the same bits_per_word value, move that logic to
> > the probe function, and let transfers default to the value defined in
> > the struct spi_device.
> >
> > Signed-off-by: Liam Beguin <lvb@...hos.com>
> Hi Liam,
>
Hi Jonathan,
> I changed the title of this one to avoid it being picked up for automated
> backporting. I don't mind if you want to request it is backported explicitly
> but it isn't a regression fix (as it never worked on such controllers) and
> is non trivial. As a result I want a backport to be a deliberate decision.
> Now titled "iio: adc: ad7949: enable use with non 14/16-bit controllers"
>
That makes sense! I'll be more careful of that in the future.
Thanks,
Liam
> This and previous applied to the togreg branch of iio.git and pushed out
> as testing for 0-day to poke at it.
>
> Thanks,
>
> Jonathan
>
> > ---
> > drivers/iio/adc/ad7949.c | 86 +++++++++++++++++++++++++++-------------
> > 1 file changed, 58 insertions(+), 28 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> > index adc4487a7d56..a263d0fcec75 100644
> > --- a/drivers/iio/adc/ad7949.c
> > +++ b/drivers/iio/adc/ad7949.c
> > @@ -14,7 +14,6 @@
> > #include <linux/bitfield.h>
> >
> > #define AD7949_CFG_MASK_TOTAL GENMASK(13, 0)
> > -#define AD7949_CFG_REG_SIZE_BITS 14
> >
> > /* CFG: Configuration Update */
> > #define AD7949_CFG_MASK_OVERWRITE BIT(13)
> > @@ -71,6 +70,7 @@ static const struct ad7949_adc_spec ad7949_adc_spec[] = {
> > * @cfg: copy of the configuration register
> > * @current_channel: current channel in use
> > * @buffer: buffer to send / receive data to / from device
> > + * @buf8b: be16 buffer to exchange data with the device in 8-bit transfers
> > */
> > struct ad7949_adc_chip {
> > struct mutex lock;
> > @@ -81,27 +81,34 @@ struct ad7949_adc_chip {
> > u16 cfg;
> > unsigned int current_channel;
> > u16 buffer ____cacheline_aligned;
> > + __be16 buf8b;
> > };
> >
> > 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,
> > - },
> > - };
> >
> > ad7949_adc->cfg = (val & mask) | (ad7949_adc->cfg & ~mask);
> > - ad7949_adc->buffer = ad7949_adc->cfg << shift;
> > - spi_message_init_with_transfers(&msg, tx, 1);
> > - ret = spi_sync(ad7949_adc->spi, &msg);
> > +
> > + switch (ad7949_adc->spi->bits_per_word) {
> > + case 16:
> > + ad7949_adc->buffer = ad7949_adc->cfg << 2;
> > + ret = spi_write(ad7949_adc->spi, &ad7949_adc->buffer, 2);
> > + break;
> > + case 14:
> > + ad7949_adc->buffer = ad7949_adc->cfg;
> > + ret = spi_write(ad7949_adc->spi, &ad7949_adc->buffer, 2);
> > + break;
> > + case 8:
> > + /* Here, type is big endian as it must be sent in two transfers */
> > + ad7949_adc->buf8b = cpu_to_be16(ad7949_adc->cfg << 2);
> > + ret = spi_write(ad7949_adc->spi, &ad7949_adc->buf8b, 2);
> > + break;
> > + default:
> > + dev_err(&ad7949_adc->indio_dev->dev, "unsupported BPW\n");
> > + return -EINVAL;
> > + }
> >
> > /*
> > * This delay is to avoid a new request before the required time to
> > @@ -116,16 +123,6 @@ 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,
> > - },
> > - };
> >
> > /*
> > * 1: write CFG for sample N and read old data (sample N-2)
> > @@ -144,9 +141,11 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,
> > }
> >
> > /* 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);
> > + if (ad7949_adc->spi->bits_per_word == 8)
> > + ret = spi_read(ad7949_adc->spi, &ad7949_adc->buf8b, 2);
> > + else
> > + ret = spi_read(ad7949_adc->spi, &ad7949_adc->buffer, 2);
> > +
> > if (ret)
> > return ret;
> >
> > @@ -158,7 +157,25 @@ 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->spi->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:
> > + /* Here, type is big endian as data was sent in two transfers */
> > + *val = be16_to_cpu(ad7949_adc->buf8b);
> > + /* 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;
> > }
> > @@ -266,6 +283,7 @@ 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;
> > @@ -292,6 +310,18 @@ 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)) {
> > + spi->bits_per_word = ad7949_adc->resolution;
> > + } else if (spi_ctrl_mask == SPI_BPW_MASK(16)) {
> > + spi->bits_per_word = 16;
> > + } else if (spi_ctrl_mask == SPI_BPW_MASK(8)) {
> > + spi->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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