linux-kernel - [PATCH] drivers: iio: adc: ltc2497: fix LSB shift

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Date:   Fri, 27 Jan 2023 14:57:14 +0200
From:   Ian Ray <ian.ray@...com>
To:     lars@...afoo.de, Michael.Hennerich@...log.com
Cc:     linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        ian.ray@...com
Subject: [PATCH] drivers: iio: adc: ltc2497: fix LSB shift

Correct the "sub_lsb" shift for both ltc2497 and ltc2499.

An earlier version of the code shifted by 14 but this was a consequence
of reading three bytes into a __be32 buffer and using be32_to_cpu(), so
eight extra bits needed to be skipped.  Now we use get_unaligned_be24()
and thus the additional skip is wrong.

Fixes 2187cfe ("drivers: iio: adc: ltc2497: LTC2499 support")
Signed-off-by: Ian Ray <ian.ray@...com>
---
 drivers/iio/adc/ltc2497.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index 17370c5..ec198c6 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -28,7 +28,6 @@ struct ltc2497_driverdata {
 	struct ltc2497core_driverdata common_ddata;
 	struct i2c_client *client;
 	u32 recv_size;
-	u32 sub_lsb;
 	/*
 	 * DMA (thus cache coherency maintenance) may require the
 	 * transfer buffers to live in their own cache lines.
@@ -65,10 +64,10 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
 		 * equivalent to a sign extension.
 		 */
 		if (st->recv_size == 3) {
-			*val = (get_unaligned_be24(st->data.d8) >> st->sub_lsb)
+			*val = (get_unaligned_be24(st->data.d8) >> 6)
 				- BIT(ddata->chip_info->resolution + 1);
 		} else {
-			*val = (be32_to_cpu(st->data.d32) >> st->sub_lsb)
+			*val = (be32_to_cpu(st->data.d32) >> 6)
 				- BIT(ddata->chip_info->resolution + 1);
 		}
 
@@ -122,7 +121,6 @@ static int ltc2497_probe(struct i2c_client *client)
 	st->common_ddata.chip_info = chip_info;
 
 	resolution = chip_info->resolution;
-	st->sub_lsb = 31 - (resolution + 1);
 	st->recv_size = BITS_TO_BYTES(resolution) + 1;
 
 	return ltc2497core_probe(dev, indio_dev);
-- 
2.10.1