[PATCH v5] amd/display: only require overlay plane to cover whole CRTC on ChromeOS

[Simon Ser <contact@emersion.fr>]

Commit ddab8bd788f5 ("drm/amd/display: Fix two cursor duplication when
using overlay") changed the atomic validation code to forbid the
overlay plane from being used if it doesn't cover the whole CRTC. The
motivation is that ChromeOS uses the atomic API for everything except
the cursor plane (which uses the legacy API). Thus amdgpu must always
be prepared to enable/disable/move the cursor plane at any time without
failing (or else ChromeOS will trip over).

As discussed in [1], there's no reason why the ChromeOS limitation
should prevent other fully atomic users from taking advantage of the
overlay plane. Let's limit the check to ChromeOS.

v4: fix ChromeOS detection (Harry)

v5: fix conflict with linux-next

[1]: https://lore.kernel.org/amd-gfx/JIQ_93_cHcshiIDsrMU1huBzx9P9LVQxucx8hQArpQu7Wk5DrCl_vTXj_Q20m_L-8C8A5dSpNcSJ8ehfcCrsQpfB5QG_Spn14EYkH9chtg0=@emersion.fr/

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Sean Paul <seanpaul@chromium.org>
Fixes: ddab8bd788f5 ("drm/amd/display: Fix two cursor duplication when using overlay")
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index f35561b5a465..2eeda1fec506 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -10594,6 +10594,31 @@ static int add_affected_mst_dsc_crtcs(struct drm_atomic_state *state, struct drm
 }
 #endif
 
+static bool is_chromeos(void)
+{
+	struct mm_struct *mm = current->mm;
+	struct file *exe_file;
+	bool ret;
+
+	/* ChromeOS renames its thread to DrmThread. Also check the executable
+	 * name. */
+	if (strcmp(current->comm, "DrmThread") != 0 || !mm)
+		return false;
+
+	rcu_read_lock();
+	exe_file = rcu_dereference(mm->exe_file);
+	if (exe_file && !get_file_rcu(exe_file))
+		exe_file = NULL;
+	rcu_read_unlock();
+
+	if (!exe_file)
+		return false;
+	ret = strcmp(exe_file->f_path.dentry->d_name.name, "chrome") == 0;
+	fput(exe_file);
+
+	return ret;
+}
+
 static int validate_overlay(struct drm_atomic_state *state)
 {
 	int i;
@@ -10601,6 +10626,10 @@ static int validate_overlay(struct drm_atomic_state *state)
 	struct drm_plane_state *new_plane_state;
 	struct drm_plane_state *primary_state, *overlay_state = NULL;
 
+	/* This is a workaround for ChromeOS only */
+	if (!is_chromeos())
+		return 0;
+
 	/* Check if primary plane is contained inside overlay */
 	for_each_new_plane_in_state_reverse(state, plane, new_plane_state, i) {
 		if (plane->type == DRM_PLANE_TYPE_OVERLAY) {
-- 
2.33.0