linux-kernel - [PATCH RFC v4 12/15] iio: adc: ad7944: don't use storagebits for sizing

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Message-Id: <20241023-dlech-mainline-spi-engine-offload-2-v4-12-f8125b99f5a1@baylibre.com>
Date: Wed, 23 Oct 2024 15:59:19 -0500
From: David Lechner <dlechner@...libre.com>
To: Mark Brown <broonie@...nel.org>, Jonathan Cameron <jic23@...nel.org>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Nuno Sá <nuno.sa@...log.com>, 
 Uwe Kleine-König <ukleinek@...nel.org>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>, 
 Lars-Peter Clausen <lars@...afoo.de>, David Jander <david@...tonic.nl>, 
 Martin Sperl <kernel@...tin.sperl.org>, linux-spi@...r.kernel.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-iio@...r.kernel.org, linux-pwm@...r.kernel.org, 
 David Lechner <dlechner@...libre.com>
Subject: [PATCH RFC v4 12/15] iio: adc: ad7944: don't use storagebits for
 sizing

Replace use of storagebits with realbits for determining the number of
bytes needed for SPI transfers.

When adding SPI offload support, storagebits will no longer be
guaranteed to be the "best fit" for 16-bit chips so we can no longer
rely on storagebits being the correct size expected by the SPI
framework. Instead, derive the correct size from realbits since it will
always be correct even when SPI offloads are used.

Signed-off-by: David Lechner <dlechner@...libre.com>
---

v4 changes: new patch in v4
---
 drivers/iio/adc/ad7944.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c
index a5aea4e9f1a7..6d1202bd55a0 100644
--- a/drivers/iio/adc/ad7944.c
+++ b/drivers/iio/adc/ad7944.c
@@ -98,6 +98,9 @@ struct ad7944_chip_info {
 	const struct iio_chan_spec channels[2];
 };
 
+/* get number of bytes for SPI xfer */
+#define AD7944_SPI_BYTES(scan_type) ((scan_type).realbits > 16 ? 4 : 2)
+
 /*
  * AD7944_DEFINE_CHIP_INFO - Define a chip info structure for a specific chip
  * @_name: The name of the chip
@@ -164,7 +167,7 @@ static int ad7944_3wire_cs_mode_init_msg(struct device *dev, struct ad7944_adc *
 
 	/* Then we can read the data during the acquisition phase */
 	xfers[2].rx_buf = &adc->sample.raw;
-	xfers[2].len = BITS_TO_BYTES(chan->scan_type.storagebits);
+	xfers[2].len = AD7944_SPI_BYTES(chan->scan_type);
 	xfers[2].bits_per_word = chan->scan_type.realbits;
 
 	spi_message_init_with_transfers(&adc->msg, xfers, 3);
@@ -193,7 +196,7 @@ static int ad7944_4wire_mode_init_msg(struct device *dev, struct ad7944_adc *adc
 	xfers[0].delay.unit = SPI_DELAY_UNIT_NSECS;
 
 	xfers[1].rx_buf = &adc->sample.raw;
-	xfers[1].len = BITS_TO_BYTES(chan->scan_type.storagebits);
+	xfers[1].len = AD7944_SPI_BYTES(chan->scan_type);
 	xfers[1].bits_per_word = chan->scan_type.realbits;
 
 	spi_message_init_with_transfers(&adc->msg, xfers, 2);
@@ -228,7 +231,7 @@ static int ad7944_chain_mode_init_msg(struct device *dev, struct ad7944_adc *adc
 	xfers[0].delay.unit = SPI_DELAY_UNIT_NSECS;
 
 	xfers[1].rx_buf = adc->chain_mode_buf;
-	xfers[1].len = BITS_TO_BYTES(chan->scan_type.storagebits) * n_chain_dev;
+	xfers[1].len = AD7944_SPI_BYTES(chan->scan_type) * n_chain_dev;
 	xfers[1].bits_per_word = chan->scan_type.realbits;
 
 	spi_message_init_with_transfers(&adc->msg, xfers, 2);
@@ -274,12 +277,12 @@ static int ad7944_single_conversion(struct ad7944_adc *adc,
 		return ret;
 
 	if (adc->spi_mode == AD7944_SPI_MODE_CHAIN) {
-		if (chan->scan_type.storagebits > 16)
+		if (chan->scan_type.realbits > 16)
 			*val = ((u32 *)adc->chain_mode_buf)[chan->scan_index];
 		else
 			*val = ((u16 *)adc->chain_mode_buf)[chan->scan_index];
 	} else {
-		if (chan->scan_type.storagebits > 16)
+		if (chan->scan_type.realbits > 16)
 			*val = adc->sample.raw.u32;
 		else
 			*val = adc->sample.raw.u16;
@@ -409,8 +412,7 @@ static int ad7944_chain_mode_alloc(struct device *dev,
 	/* 1 word for each voltage channel + aligned u64 for timestamp */
 
 	chain_mode_buf_size = ALIGN(n_chain_dev *
-		BITS_TO_BYTES(chan[0].scan_type.storagebits), sizeof(u64))
-		+ sizeof(u64);
+		AD7944_SPI_BYTES(chan[0].scan_type), sizeof(u64)) + sizeof(u64);
 	buf = devm_kzalloc(dev, chain_mode_buf_size, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;

-- 
2.43.0