linux-kernel - [PATCH] iio: adc: ad7606: explicit timestamp alignment

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Message-Id: <20250428-iio-adc-ad7606-fix-buffer-alignment-v1-1-88dfc57e5df0@baylibre.com>
Date: Mon, 28 Apr 2025 21:17:14 -0500
From: David Lechner <dlechner@...libre.com>
To: Michael Hennerich <Michael.Hennerich@...log.com>, 
 Jonathan Cameron <jic23@...nel.org>, 
 Nuno Sá <nuno.sa@...log.com>, 
 Andy Shevchenko <andy@...nel.org>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] iio: adc: ad7606: explicit timestamp alignment

Use struct with aligned_s64 timestamp to make timestamp alignment
explicit. Technically, what we have works because for all known
architectures, IIO_DMA_MINALIGN is a multiple of __alignof__(s64).
But this way, we don't have to make people read the comments to know
why there are extra elements in each buffer.

---
 drivers/iio/adc/ad7606.h | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/ad7606.h b/drivers/iio/adc/ad7606.h
index 89d49551eaf515bab9706c12bff056dfcb707b67..441e62c521bcbea69b4f70bb2d55f65334d22276 100644
--- a/drivers/iio/adc/ad7606.h
+++ b/drivers/iio/adc/ad7606.h
@@ -155,12 +155,15 @@ struct ad7606_state {
 	/*
 	 * DMA (thus cache coherency maintenance) may require the
 	 * transfer buffers to live in their own cache lines.
-	 * 16 * 16-bit samples + 64-bit timestamp - for AD7616
-	 * 8 * 32-bit samples + 64-bit timestamp - for AD7616C-18 (and similar)
+	 * 16 * 16-bit samples for AD7616
+	 * 8 * 32-bit samples for AD7616C-18 (and similar)
 	 */
-	union {
-		u16 buf16[20];
-		u32 buf32[10];
+	struct {
+		union {
+			u16 buf16[16];
+			u32 buf32[8];
+		};
+		aligned_s64 timestamp;
 	} data __aligned(IIO_DMA_MINALIGN);
 	__be16				d16[2];
 };

---
base-commit: b475195fecc79a1a6e7fb0846aaaab0a1a4cb2e6
change-id: 20250428-iio-adc-ad7606-fix-buffer-alignment-9fcde71687dc

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