staging: iio: resolver: ad2s1210: always use 16-bit value for raw read

This removes the special handling for resolutions lower than 16 bits.
This will allow us to use a fixed scale independent of the resolution.

A new sample field is added to store the raw data instead of reusing
the config mode rx buffer so that we don't have to do a cast or worry
about unaligned access.

Also, for the record, according to the datasheet, the logic for the
special handling based on hysteresis that was removed was incorrect.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20230929-ad2s1210-mainline-v3-7-fa4364281745@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/staging/iio/resolver/ad2s1210.c b/drivers/staging/iio/resolver/ad2s1210.c
index 832f86bf15e577e5e42f493f46c607f4ad28d821..f9774dff2df4df5d27bcc01945e60ce59968483d 100644 (file)
--- a/drivers/staging/iio/resolver/ad2s1210.c
+++ b/drivers/staging/iio/resolver/ad2s1210.c
@@ -95,7 +95,11 @@ struct ad2s1210_state {
        bool hysteresis;
        u8 resolution;
        enum ad2s1210_mode mode;
-       u8 rx[2] __aligned(IIO_DMA_MINALIGN);
+       /** For reading raw sample value via SPI. */
+       __be16 sample __aligned(IIO_DMA_MINALIGN);
+       /** SPI transmit buffer. */
+       u8 rx[2];
+       /** SPI receive buffer. */
        u8 tx[2];
 };
 
@@ -464,10 +468,7 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
                             long m)
 {
        struct ad2s1210_state *st = iio_priv(indio_dev);
-       u16 negative;
        int ret = 0;
-       u16 pos;
-       s16 vel;
 
        mutex_lock(&st->lock);
        gpiod_set_value(st->gpios[AD2S1210_SAMPLE], 0);
@@ -487,26 +488,17 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
        }
        if (ret < 0)
                goto error_ret;
-       ret = spi_read(st->sdev, st->rx, 2);
+       ret = spi_read(st->sdev, &st->sample, 2);
        if (ret < 0)
                goto error_ret;
 
        switch (chan->type) {
        case IIO_ANGL:
-               pos = be16_to_cpup((__be16 *)st->rx);
-               if (st->hysteresis)
-                       pos >>= 16 - st->resolution;
-               *val = pos;
+               *val = be16_to_cpu(st->sample);
                ret = IIO_VAL_INT;
                break;
        case IIO_ANGL_VEL:
-               vel = be16_to_cpup((__be16 *)st->rx);
-               vel >>= 16 - st->resolution;
-               if (vel & 0x8000) {
-                       negative = (0xffff >> st->resolution) << st->resolution;
-                       vel |= negative;
-               }
-               *val = vel;
+               *val = (s16)be16_to_cpu(st->sample);
                ret = IIO_VAL_INT;
                break;
        default: