linux-kernel - [PATCH v6 1/7] iio: make IIO_DMA

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Message-Id: <20250507-iio-introduce-iio_declare_buffer_with_ts-v6-1-4aee1b9f1b89@baylibre.com>
Date: Wed, 07 May 2025 15:42:40 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>, 
 David Lechner <dlechner@...libre.com>, 
 Nuno Sá <nuno.sa@...log.com>, 
 Andy Shevchenko <andy@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>, 
 Michael Hennerich <Michael.Hennerich@...log.com>, 
 Eugen Hristev <eugen.hristev@...aro.org>, 
 Nicolas Ferre <nicolas.ferre@...rochip.com>, 
 Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 Claudiu Beznea <claudiu.beznea@...on.dev>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v6 1/7] iio: make IIO_DMA_MINALIGN minimum of 8 bytes

Add a condition to ensure that IIO_DMA_MINALIGN is at least 8 bytes.
On some 32-bit architectures, IIO_DMA_MINALIGN is 4. In many cases,
drivers are using this alignment for buffers that include a 64-bit
timestamp that is used with iio_push_to_buffers_with_ts(), which expects
the timestamp to be aligned to 8 bytes. To handle this, we can just make
IIO_DMA_MINALIGN at least 8 bytes.

Reviewed-by: Nuno Sá <nuno.sa@...log.com>
Signed-off-by: David Lechner <dlechner@...libre.com>
---

v6 changes:
- Removed the #if and use MAX instead since apparently clang raises an
  error that __alignof__ isn't defined when used in a #if condition.
---
 include/linux/iio/iio.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 638cf2420fbd85cf2924d09d061df601d1d4bb2a..a574f22398e45cad1ea741d20d302f88756a1b13 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -10,6 +10,7 @@
 #include <linux/device.h>
 #include <linux/cdev.h>
 #include <linux/compiler_types.h>
+#include <linux/minmax.h>
 #include <linux/slab.h>
 #include <linux/iio/types.h>
 /* IIO TODO LIST */
@@ -775,8 +776,14 @@ static inline void *iio_device_get_drvdata(const struct iio_dev *indio_dev)
  * to in turn include IIO_DMA_MINALIGN'd elements such as buffers which
  * must not share  cachelines with the rest of the structure, thus making
  * them safe for use with non-coherent DMA.
+ *
+ * A number of drivers also use this on buffers that include a 64-bit timestamp
+ * that is used with iio_push_to_buffer_with_ts(). Therefore, in the case where
+ * DMA alignment is not sufficient for proper timestamp alignment, we align to
+ * 8 bytes instead.
  */
-#define IIO_DMA_MINALIGN ARCH_DMA_MINALIGN
+#define IIO_DMA_MINALIGN MAX(ARCH_DMA_MINALIGN, sizeof(s64))
+
 struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv);
 
 /* The information at the returned address is guaranteed to be cacheline aligned */

-- 
2.43.0