[PATCH v2] drm/ast: Don't check new mode if CRTC is being disabled

[Thomas Zimmermann]

Suspending failed because there's no mode if the CRTC is being
disabled. Early-out in this case. This fixes runtime PM for ast.

v2:
	* add Tested-by/Reviewed-by tags
	* add Fixes tags and CC (Sam)
	* improved comment

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Reported-by: Cary Garrett <cogarre at gmail.com>
Tested-by: Cary Garrett <cogarre at gmail.com>
Fixes: b48e1b6ffd28 ("drm/ast: Add CRTC helpers for atomic modesetting")
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Sam Ravnborg <sam at ravnborg.org>
Cc: <stable at vger.kernel.org> # v5.6+
---
 drivers/gpu/drm/ast/ast_mode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 7a9f20a2fd303..0cbbb21edb4e1 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -801,6 +801,9 @@ static int ast_crtc_helper_atomic_check(struct drm_crtc *crtc,
 		return -EINVAL;
 	}
 
+	if (!state->enable)
+		return 0; /* no mode checks if CRTC is being disabled */
+
 	ast_state = to_ast_crtc_state(state);
 
 	format = ast_state->format;
-- 
2.26.0