[PATCH] drm/amd/display: Don't set mode_changed=false if the stream was removed

[Harry Wentland]

On 2019-05-30 3:51 p.m., Nicholas Kazlauskas wrote:
> [Why]
> When switching from vt to desktop with EDID emulation we can receive
> an atomic commit such that we have a crtc where mode_changed = true.
> 
> During the dm_update_crtc_state disable pass we remove the stream from
> the context and free it on the dm_new_crtc_state.
> 
> During the enable pass we compare the new provisional stream to the
> dm_old_crtc_state->stream and determine that the stream is unchanged
> and no scaling has been changed.
> 
> Following this, new_crtc_state->mode_changed is then set to false.
> The connectors haven't changed and the CRTC active state hasn't changed
> so drm_atomic_crtc_needs_modeset returns false, so we jump to
> skip_modeset and we hit:
> 
> BUG_ON(dm_new_crtc_state->stream == NULL);
> 
> ...since the old stream is gone from the context and the new stream is
> also still NULL.
> 
> [How]
> Ensure that we still a stream to reuse before checking if we can reuse
> the old stream without a full modeset.
> 
> Cc: Roman Li <Roman.Li at amd.com>
> Cc: Leo Li <sunpeng.li at amd.com>
> Cc: Harry Wentland <Harry.Wentland at amd.com>
> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>

Reviewed-by: Harry Wentland <harry.wentland at amd.com>

Harry

> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> 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 57359037ed7c..796f83ca7a4c 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -6248,7 +6248,17 @@ static int dm_update_crtc_state(struct amdgpu_display_manager *dm,
>  
>  		dm_new_crtc_state->abm_level = dm_new_conn_state->abm_level;
>  
> -		if (dc_is_stream_unchanged(new_stream, dm_old_crtc_state->stream) &&
> +		/*
> +		 * If we already removed the old stream from the context
> +		 * (and set the new stream to NULL) then we can't reuse
> +		 * the old stream even if the stream and scaling are unchanged.
> +		 * We'll hit the BUG_ON and black screen.
> +		 *
> +		 * TODO: Refactor this function to allow this check to work
> +		 * in all conditions.
> +		 */
> +		if (dm_new_crtc_state->stream &&
> +		    dc_is_stream_unchanged(new_stream, dm_old_crtc_state->stream) &&
>  		    dc_is_stream_scaling_unchanged(new_stream, dm_old_crtc_state->stream)) {
>  			new_crtc_state->mode_changed = false;
>  			DRM_DEBUG_DRIVER("Mode change not required, setting mode_changed to %d",
>