[PATCH] drm/simple-kms: Drop drm_simple_kms_format_mod_supported.

[Mario Kleiner]

The check was introduced to make sure that only the
DRM_FORMAT_MOD_LINEAR modifier is accepted by tinydrm.

However, if .format_mod_supported is not hooked up to
drm_simple_kms_format_mod_supported then the core will
simply validate modifiers against the format_modifiers
list passed into drm_simple_display_pipe_init() or
drm_universal_plane_init() and perform the same validation
as drm_simple_kms_format_mod_supported() would have done.

Additionally, if a kms driver / plane does not support
modifiers, it will not reject fb updates with no modifiers/
DRM_FORMAT_MOD_INVALID. This is important, because some
simple drm drivers, e.g., pl111, pass NULL as format_modifiers
list, so modifier support is disabled for these drivers,
userspace would fall back to drmAddFB() without modifiers,
and ergo the current drm_simple_kms_format_mod_supported()
function would reject valid modifier-less fb's.

So this should fix display on non-tinydrm drivers like
pl111, and probably also for non-atomic clients?

The Mesa vc4 gallium driver mentions pl111 as one possible
display driver in render_only mode, so i assume this matters
for some SoC's?

The background for the patch that introduced this was to
fix atomic modesetting in the X-Servers modesetting-ddx,
but with atomic modesetting and format modifiers disabled
in modesetting-ddx (and also current kernels when interacting
with modesetting-ddx), i assume this should fix some panels.

Note that i don't have any of the hw required for testing
this, this is purely based on looking at the code, so this
patch is only compile-tested.

For more reference, this fix was motivated by some discussions
around broken page-flipping on VideoCore6 / RaspberryPi 4
with current Raspbian OS, so the experts may want to weigh
in on that Mesa bug report as well, under the following link:

https://gitlab.freedesktop.org/mesa/mesa/-/issues/3601

Fixes: dff906c3f91c ("drm/tinydrm: Advertise that we can do only DRM_FORMAT_MOD_LINEAR.")
Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
Cc: Eric Anholt <eric at anholt.net>
Cc: Noralf Trønnes <noralf at tronnes.org>
Cc: Maxime Ripard <mripard at kernel.org>
---
 drivers/gpu/drm/drm_simple_kms_helper.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
index 743e57c1b44f..5f3e30553172 100644
--- a/drivers/gpu/drm/drm_simple_kms_helper.c
+++ b/drivers/gpu/drm/drm_simple_kms_helper.c
@@ -229,13 +229,6 @@ static void drm_simple_kms_plane_cleanup_fb(struct drm_plane *plane,
 	pipe->funcs->cleanup_fb(pipe, state);
 }
 
-static bool drm_simple_kms_format_mod_supported(struct drm_plane *plane,
-						uint32_t format,
-						uint64_t modifier)
-{
-	return modifier == DRM_FORMAT_MOD_LINEAR;
-}
-
 static const struct drm_plane_helper_funcs drm_simple_kms_plane_helper_funcs = {
 	.prepare_fb = drm_simple_kms_plane_prepare_fb,
 	.cleanup_fb = drm_simple_kms_plane_cleanup_fb,
@@ -250,7 +243,6 @@ static const struct drm_plane_funcs drm_simple_kms_plane_funcs = {
 	.reset			= drm_atomic_helper_plane_reset,
 	.atomic_duplicate_state	= drm_atomic_helper_plane_duplicate_state,
 	.atomic_destroy_state	= drm_atomic_helper_plane_destroy_state,
-	.format_mod_supported   = drm_simple_kms_format_mod_supported,
 };
 
 /**
-- 
2.25.1