On Sun, 01 Aug 2021 19:01:10 -0400
"Liam Beguin" [off-list ref] wrote:

On Sat Jul 31, 2021 at 10:52 AM EDT, Jonathan Cameron wrote:

quoted

On Sat, 31 Jul 2021 15:29:21 +0100
Jonathan Cameron [off-list ref] wrote:
 

quoted

On Tue, 27 Jul 2021 19:29:03 -0400
Liam Beguin [off-list ref] wrote:
  

quoted

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>
---
 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
  

quoted

 	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.  

Understood, I'll go with your suggestion.

Out of curiosity, other that being more explicit, is there another
we'd rather not use {get,put}_unaligned_be16()?

We know it is aligned (as u16) so on a big endian platform that happens
to not handle unaligned accesses we will now be doing work which wouldn't
be needed if there was a get_aligned_be16() that was more relaxed about
types than cpu_to_be16() etc.

So basically it looks odd and we will will be hiding that we are smashing
data of potentially different ordering into the same structure field.

quoted

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.  

Noted, Thanks for taking the time to explaining this.

Liam

quoted

Jonathan
   

quoted

quoted

+		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");