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Date: Sat, 31 Jul 2021 15:52:28 +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 v4 2/5] iio: adc: ad7949: fix spi messages on non 14-bit
controllers
On Sat, 31 Jul 2021 15:29:21 +0100
Jonathan Cameron <jic23@...nel.org> wrote:
> On Tue, 27 Jul 2021 19:29:03 -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>
> > ---
> > drivers/iio/adc/ad7949.c | 62 ++++++++++++++++++++++++++++++++++------
> > 1 file changed, 54 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> > index 0b549b8bd7a9..f1702c54c8be 100644
> > --- a/drivers/iio/adc/ad7949.c
> > +++ b/drivers/iio/adc/ad7949.c
> > @@ -67,6 +67,7 @@ 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 +78,7 @@ 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 +88,34 @@ 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;
>
> The define for this was removed in patch 1. I'll fix that up whilst applying by
> keeping it until this patch. Please check build passes on intermediate points
> during a patch series as otherwise we may break bisectability and that's really
> annoying if you are bisecting!
>
> Jonathan
>
> > 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:
> > + /* Here, type is big endian as it must be sent in two transfers */
> > + ad7949_adc->buffer = (u16)cpu_to_be16(ad7949_adc->cfg << 2);
Gah, I wasn't thinking clearly when I suggested this. Sparse warns on the
endian conversion
One option is to resort to ignoring the fact we know it's aligned and
use the put_unaligned_be16() and get_unaligned_be16 calls which sparse seems to be
happy with. Alternative would be to just have a be16 buffer after the existing
one in the iio_priv structure. Then you will have to change the various users
of iio_priv()->buffer to point to the new value if we are doing 8 bit transfers.
Whilst more invasive, this second option is the one I'd suggest.
Note that there will be no need to add an __cacheline_aligned marking to this
new element because it will be in a cachline that is only used for DMA simply being
after the other buffer element which is force to start on a new cacheline.
Jonathan
> > + 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 +132,12 @@ 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,
> > },
> > };
> >
> > @@ -157,7 +172,25 @@ 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->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->buffer);
> > + /* 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 +298,7 @@ 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 +325,18 @@ 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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