drm_panthor_gpu_info::shader_present is currently automatically offset
by 4 byte to meet Arm's 32-bit/64-bit field alignment rules, but those
constraints don't stand on 32-bit x86 and cause a mismatch when running
an x86 binary in a user emulated environment like FEX. It's also
generally agreed that uAPIs should explicitly pad their struct fields,
which we originally intended to do, but a mistake slipped through during
the submission process, leading drm_panthor_gpu_info::shader_present to
be misaligned.
This uAPI change doesn't break any of the existing users of panthor
which are either arm32 or arm64 where the 64-bit alignment of
u64 fields is already enforced a the compiler level.
Changes in v2:
- Rename the garbage field into pad0 and adjust the comment accordingly
- Add Liviu's A-b
Changes in v3:
- Add R-bs
Fixes: 0f25e493a246 ("drm/panthor: Add uAPI")
Signed-off-by: Boris Brezillon <boris.brezil...@collabora.com>
Acked-by: Liviu Dudau <liviu.du...@arm.com>
Reviewed-by: Adrián Larumbe <adrian.laru...@collabora.com>
Reviewed-by: Steven Price <steven.pr...@arm.com>
---
include/uapi/drm/panthor_drm.h | 3 +++
1 file changed, 3 insertions(+)
diff --git a/include/uapi/drm/panthor_drm.h b/include/uapi/drm/panthor_drm.h
index ad9a70afea6c..3a76c4f2882b 100644
--- a/include/uapi/drm/panthor_drm.h
+++ b/include/uapi/drm/panthor_drm.h
@@ -296,6 +296,9 @@ struct drm_panthor_gpu_info {
/** @as_present: Bitmask encoding the number of address-space exposed
by the MMU. */
__u32 as_present;
+ /** @pad0: MBZ. */
+ __u32 pad0;
+
/** @shader_present: Bitmask encoding the shader cores exposed by the
GPU. */
__u64 shader_present;
--
2.49.0
