Re: [PATCH v3 10/11] drm: Use state helper instead of the plane state pointer

[Stephen Boyd <swboyd@chromium.org>]

Trimming Cc list way down, sorry if that's too much.

Quoting Maxime Ripard (2021-02-19 04:00:30)
> Many drivers reference the plane->state pointer in order to get the
> current plane state in their atomic_update or atomic_disable hooks,
> which would be the new plane state in the global atomic state since
> _swap_state happened when those hooks are run.

Does this mean drm_atomic_helper_swap_state()?

> 
> Use the drm_atomic_get_new_plane_state helper to get that state to make it
> more obvious.
> 
> This was made using the coccinelle script below:
> 
> @ plane_atomic_func @
> identifier helpers;
> identifier func;
> @@
> 
> (
>  static const struct drm_plane_helper_funcs helpers = {
>         ...,
>         .atomic_disable = func,
>         ...,
>  };
> |
>  static const struct drm_plane_helper_funcs helpers = {
>         ...,
>         .atomic_update = func,
>         ...,
>  };
> )
> 
> @ adds_new_state @
> identifier plane_atomic_func.func;
> identifier plane, state;
> identifier new_state;
> @@
> 
>  func(struct drm_plane *plane, struct drm_atomic_state *state)
>  {
>         ...
> -       struct drm_plane_state *new_state = plane->state;
> +       struct drm_plane_state *new_state = drm_atomic_get_new_plane_state(state, plane);
>         ...
>  }
> 
> @ include depends on adds_new_state @
> @@
> 
>  #include <drm/drm_atomic.h>
> 
> @ no_include depends on !include && adds_new_state @
> @@
> 
> + #include <drm/drm_atomic.h>
>   #include <drm/...>
> 
>  drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c       | 3 ++-
>  drivers/gpu/drm/msm/disp/mdp4/mdp4_plane.c      | 4 +++-
>  drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c      | 3 ++-
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> index 31071f9e21d7..e8ce72fe54a4 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> @@ -1244,7 +1244,8 @@ static void dpu_plane_atomic_update(struct drm_plane *plane,
>                                 struct drm_atomic_state *state)
>  {
>         struct dpu_plane *pdpu = to_dpu_plane(plane);
> -       struct drm_plane_state *new_state = plane->state;
> +       struct drm_plane_state *new_state = drm_atomic_get_new_plane_state(state,
> +                                                                          plane);
>  
>         pdpu->is_error = false;
>  

This is oopsing for me. It turns out that 'new_state' is NULL. According
to the comments drm_atomic_get_new_plane_state() can return NULL if the
plane isn't part of the global state. I haven't looked much further but
wanted to report it here in case that type of return value makes sense.

If I revert this patch from linux-next my display works and doesn't
crash the system. Or I can check for NULL in the if below and it also
works.

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
index df7f3d3afd8b..f31b89531f6a 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
@@ -1251,7 +1251,7 @@ static void dpu_plane_atomic_update(struct drm_plane *plane,
 
 	DPU_DEBUG_PLANE(pdpu, "\n");
 
-	if (!new_state->visible) {
+	if (new_state && !new_state->visible) {
 		_dpu_plane_atomic_disable(plane);
 	} else {
 		dpu_plane_sspp_atomic_update(plane);