[PATCH] drm/udl: Restore display mode on resume

[Daniel Vetter]

On Thu, Jul 28, 2022 at 09:31:09AM +0200, Thomas Zimmermann wrote:
> Restore the display mode whne resuming from suspend. Currently, the
> display remains dark.
> 
> On resume, the CRTC's mode does not change, but the 'active' flag
> changes to 'true'. Taking this into account when considering a mode
> switch restores the display mode.
> 
> The bug is reproducable by using Gnome with udl and observing the
> adapter's suspend/resume behavior.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>  drivers/gpu/drm/udl/udl_modeset.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/udl/udl_modeset.c b/drivers/gpu/drm/udl/udl_modeset.c
> index e67c40a48fb4..bf17f38fdb54 100644
> --- a/drivers/gpu/drm/udl/udl_modeset.c
> +++ b/drivers/gpu/drm/udl/udl_modeset.c
> @@ -8,6 +8,7 @@
>   * Copyright (C) 2009 Bernie Thompson <bernie at plugable.com>
>   */
>  
> +#include <drm/drm_atomic.h>
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_crtc_helper.h>
>  #include <drm/drm_damage_helper.h>
> @@ -382,7 +383,7 @@ udl_simple_display_pipe_enable(struct drm_simple_display_pipe *pipe,
>  
>  	udl_handle_damage(fb, &shadow_plane_state->data[0], 0, 0, fb->width, fb->height);
>  
> -	if (!crtc_state->mode_changed)
> +	if (!drm_atomic_crtc_needs_modeset(crtc_state))
>  		return;

The helpers shouldn't even call you in this case. Which means you
should outright remove this check. I think this simple dates back to the
old legacy crtc helper implementation, where stuff like this was necessary
because the crtc helpers just loved to disable you multiple times.

Looking at git history this seems to have been a regression introduced by 
997d33c35618 ("drm/udl: Inline DPMS code into CRTC enable and disable functions")

So you need cc: stable here and all that. And before this change there was
no such check either, so we don't need to backport if further.

Since this seems to have been stuck for a while here's my upfront

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

for v2 with all these changes applied.
-Daniel

>  
>  	/* enable display */
> -- 
> 2.37.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch