[PATCH v2] iio: adc: ti-ads7950: use iio_push_to_buffers_with_ts_unaligned()

David Lechner
2026-03-14T21:12:42Z

Use iio_push_to_buffers_with_ts_unaligned() to avoid unaligned access
when writing the timestamp in the rx_buf.

The previous implementation would have been fine on architectures that
support 4-byte alignment of 64-bit integers but could cause issues on
architectures that require 8-byte alignment.

Fixes: 902c4b2446d4 ("iio: adc: New driver for TI ADS7950 chips")
Signed-off-by: David Lechner <dlechner@baylibre.com>
---
Since we were looking at this driver, I was going to convert this to use
IIO_DECLARE_DMA_BUFFER_WITH_TS() but then I noticed that we actually
have an unaligned access problem with the timestamp since we are
ignoring the first two elements in the rx_buf when pushing the data to
the buffer.

Unfortunately, this will cause a merge conflict with the series Dmitry
is working on. I don't think there is any rush to get this backported
since no one has reported a crash from unaligned access. Since fixes
should go before improvements, we could apply this to iio/togreg then
Dmitry can rebase his series on top of it.
---
Changes in v2:
- use sizeof(*st->rx_buf)
- Link to v1: https://patch.msgid.link/20260307-iio-adc-ti-ads7950-declare-dma-buffer-v1-1-79b1309338df@baylibre.com
---
drivers/iio/adc/ti-ads7950.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/adc/ti-ads7950.c b/drivers/iio/adc/ti-ads7950.c
index cdc624889559..418452aaca81 100644
--- a/drivers/iio/adc/ti-ads7950.c
+++ b/drivers/iio/adc/ti-ads7950.c
@@ -47,8 +47,6 @@
#define TI_ADS7950_MAX_CHAN 16
#define TI_ADS7950_NUM_GPIOS 4

-#define TI_ADS7950_TIMESTAMP_SIZE (sizeof(int64_t) / sizeof(__be16))
-
/* val = value, dec = left shift, bits = number of bits of the mask */
#define TI_ADS7950_EXTRACT(val, dec, bits) \
(((val) >> (dec)) & ((1 << (bits)) - 1))
@@ -105,8 +103,7 @@ struct ti_ads7950_state {
* DMA (thus cache coherency maintenance) may require the
* transfer buffers to live in their own cache lines.
*/
- u16 rx_buf[TI_ADS7950_MAX_CHAN + 2 + TI_ADS7950_TIMESTAMP_SIZE]
- __aligned(IIO_DMA_MINALIGN);
+ u16 rx_buf[TI_ADS7950_MAX_CHAN + 2] __aligned(IIO_DMA_MINALIGN);
u16 tx_buf[TI_ADS7950_MAX_CHAN + 2];
u16 single_tx;
u16 single_rx;
@@ -313,8 +310,10 @@ static irqreturn_t ti_ads7950_trigger_handler(int irq, void *p)
if (ret < 0)
goto out;

- iio_push_to_buffers_with_timestamp(indio_dev, &st->rx_buf[2],
- iio_get_time_ns(indio_dev));
+ iio_push_to_buffers_with_ts_unaligned(indio_dev, &st->rx_buf[2],
+ sizeof(*st->rx_buf) *
+ TI_ADS7950_MAX_CHAN,
+ iio_get_time_ns(indio_dev));

out:
mutex_unlock(&st->slock);

---
base-commit: 79a86a6cc3669416a21fef32d0767d39ba84b3aa
change-id: 20260307-iio-adc-ti-ads7950-declare-dma-buffer-9d5269ffa8bb

Best regards,
--
David Lechner <dlechner@baylibre.com>