From 4c70ac7639f6af6d7c2d01f0307665a4b9afada7 Mon Sep 17 00:00:00 2001
From: Eric Anholt <eric@anholt.net>
Date: Mon, 30 Apr 2018 16:59:27 -0700
Subject: drm/vc4: Add a pad field to align drm_vc4_submit_cl to 64 bits.

I had originally asked Stefan Schake to drop the pad field from the
syncobj changes that just landed, because I couldn't come up with a
reason to align to 64 bits.

Talking with Dave Airlie about the new v3d driver's submit ioctl, we
came up with a reason: sizeof() on 64-bit platforms may align to 64
bits, in which case the userspace will be submitting the aligned size
and the final 32 bits won't be zero-padded by the kernel.  If
userspace doesn't zero-fill, then a future ABI change adding a 32-bit
field at the end could potentially cause the kernel to read undefined
data from old userspace (our userspace happens to use structure
initialization that zero-fills, but as a general rule we try not to
rely on that in the kernel).

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20180430235927.28712-1-eric@anholt.net
Reviewed-by: Stefan Schake <stschake@gmail.com>
---
 include/uapi/drm/vc4_drm.h | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'include')

diff --git a/include/uapi/drm/vc4_drm.h b/include/uapi/drm/vc4_drm.h
index 2be4fe3610b8..2cac6277a1d7 100644
--- a/include/uapi/drm/vc4_drm.h
+++ b/include/uapi/drm/vc4_drm.h
@@ -193,6 +193,8 @@ struct drm_vc4_submit_cl {
 	 * render job. 0 means ignore.
 	 */
 	__u32 out_sync;
+
+	__u32 pad2;
 };
 
 /**
-- 
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