linux-kernel - [PATCH] media: uvcvideo: Explicit alignment of uvc_frame and uvc

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Message-Id: <20230501-uvc-align-v1-1-0f713e4b84c3@chromium.org>
Date:   Mon, 01 May 2023 16:49:31 +0200
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH] media: uvcvideo: Explicit alignment of uvc_frame and
 uvc_format

Struct uvc_frame and uvc_format are packaged together on
streaming->formats on a sigle allocation.

This is working fine because both structures have a field with a
pointer, but it will stop working when the sizeof() of any of those
structs is not a muliple of the sizeof(void*).

Make that aligment contract explicit.

Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
This is better than 3 allocations, and do not have any performance
penalty.
---
 drivers/media/usb/uvc/uvcvideo.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index 9a596c8d894a..03e8a543c8e6 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -252,7 +252,7 @@ struct uvc_frame {
 	u8  bFrameIntervalType;
 	u32 dwDefaultFrameInterval;
 	u32 *dwFrameInterval;
-};
+} __aligned(sizeof(void *)); /* uvc_frame is packed on streaming->formats. */
 
 struct uvc_format {
 	u8 type;
@@ -266,7 +266,7 @@ struct uvc_format {
 
 	unsigned int nframes;
 	struct uvc_frame *frame;
-};
+} __aligned(sizeof(void *)); /* uvc_format is packed on streaming->formats. */
 
 struct uvc_streaming_header {
 	u8 bNumFormats;

---
base-commit: 58390c8ce1bddb6c623f62e7ed36383e7fa5c02f
change-id: 20230501-uvc-align-6ff202b68dab

Best regards,
-- 
Ricardo Ribalda <ribalda@...omium.org>