[PATCH] drm/amd/display: Fix pageflipping for XOrg in Linux 5.11+

[Mario Kleiner]

Commit 816853f9dc4057b6c7ee3c45ca9bd5905 ("drm/amd/display: Set new
format info for converted metadata.") may fix the getfb2 ioctl, but
in exchange it completely breaks all pageflipping for classic user
space, e.g., XOrg, as tested with both amdgpu-ddx and modesetting-ddx.
This leads to massive tearing, broken visual timing/timestamping etc.

Reason is that the classic pageflip ioctl doesn't allow a fb format
change during flip, and at least X uses classic pageflip ioctl and no
atomic modesetting api at all.

As one attempted workaround, only set the new format info for converted
metadata if the calling client isn't X. Not sure if this is the best
way, or if a better check would not be "not all atomic clients" or
similar? In any case it works for XOrg X-Server. Checking the ddx
code of intel-ddx/modesetting-ddx/amdgpu-ddx as well as grepping over
Mesa doesn't show any users of the getfb2 ioctl(), so the need for this
format info assignment seems to be more the exception than the rule?

Fixes: 816853f9dc40 ("drm/amd/display: Set new format info for converted metadata.")
Cc: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
Cc: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
index f764803c53a4..cb414b3d327a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
@@ -828,7 +828,8 @@ static int convert_tiling_flags_to_modifier(struct amdgpu_framebuffer *afb)
 			if (!format_info)
 				return -EINVAL;
 
-			afb->base.format = format_info;
+			if (afb->base.comm[0] != 'X')
+				afb->base.format = format_info;
 		}
 	}
 
-- 
2.25.1