Boris Brezillon <boris.brezil...@bootlin.com> writes:

> We are about to use vc4_plane_mode_set() in the async check path, and
> async updates require that LBM size stay the same since they reuse the
> LBM from the previous state. So we definitely don't want to allocate a
> new LBM region that we know for sure will be free right away.
>
> Move the LBM allocation out of vc4_plane_mode_set() and call the new
> function (vc4_plane_update_lbm()) from vc4_plane_atomic_check().
>
> Signed-off-by: Boris Brezillon <boris.brezil...@bootlin.com>
> ---
>  drivers/gpu/drm/vc4/vc4_drv.h   |  1 +
>  drivers/gpu/drm/vc4/vc4_plane.c | 82 ++++++++++++++++++++++-----------
>  2 files changed, 55 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
> index bd6ef1f31822..9ed05fb61eb6 100644
> --- a/drivers/gpu/drm/vc4/vc4_drv.h
> +++ b/drivers/gpu/drm/vc4/vc4_drv.h
> @@ -338,6 +338,7 @@ struct vc4_plane_state {
>       u32 pos0_offset;
>       u32 pos2_offset;
>       u32 ptr0_offset;
> +     u32 lbm_offset;
>  
>       /* Offset where the plane's dlist was last stored in the
>        * hardware at vc4_crtc_atomic_flush() time.
> diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
> index f6e3e8d33115..392a51f2bf8f 100644
> --- a/drivers/gpu/drm/vc4/vc4_plane.c
> +++ b/drivers/gpu/drm/vc4/vc4_plane.c
> @@ -452,6 +452,43 @@ static void vc4_write_scaling_parameters(struct 
> drm_plane_state *state,
>       }
>  }
>  
> +static int vc4_plane_update_lbm(struct drm_plane_state *state)
> +{
> +     struct vc4_dev *vc4 = to_vc4_dev(state->plane->dev);
> +     struct vc4_plane_state *vc4_state = to_vc4_plane_state(state);
> +     unsigned long irqflags;
> +     u32 lbm_size;
> +
> +     lbm_size = vc4_lbm_size(state);
> +     if (!lbm_size)
> +             return 0;
> +
> +     if (WARN_ON(!vc4_state->lbm_offset))
> +             return -EINVAL;
> +
> +     /* Allocate the LBM memory that the HVS will use for temporary
> +      * storage due to our scaling/format conversion.
> +      */
> +     if (!vc4_state->lbm.allocated) {
> +             int ret;
> +
> +             spin_lock_irqsave(&vc4->hvs->mm_lock, irqflags);
> +             ret = drm_mm_insert_node_generic(&vc4->hvs->lbm_mm,
> +                                              &vc4_state->lbm,
> +                                              lbm_size, 32, 0, 0);
> +             spin_unlock_irqrestore(&vc4->hvs->mm_lock, irqflags);
> +
> +             if (ret)
> +                     return ret;
> +     } else {
> +             WARN_ON_ONCE(lbm_size != vc4_state->lbm.size);
> +     }
> +
> +     vc4_state->dlist[vc4_state->lbm_offset] = vc4_state->lbm.start;
> +
> +     return 0;
> +}
> +
>  /* Writes out a full display list for an active plane to the plane's
>   * private dlist state.
>   */
> @@ -469,31 +506,12 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
>       bool mix_plane_alpha;
>       bool covers_screen;
>       u32 scl0, scl1, pitch0;
> -     u32 lbm_size, tiling;
> -     unsigned long irqflags;
> +     u32 tiling;
>       u32 hvs_format = format->hvs;
>       int ret, i;
>  
> -     ret = vc4_plane_setup_clipping_and_scaling(state);
> -     if (ret)
> -             return ret;
> -
> -     /* Allocate the LBM memory that the HVS will use for temporary
> -      * storage due to our scaling/format conversion.
> -      */
> -     lbm_size = vc4_lbm_size(state);
> -     if (lbm_size) {
> -             if (!vc4_state->lbm.allocated) {
> -                     spin_lock_irqsave(&vc4->hvs->mm_lock, irqflags);
> -                     ret = drm_mm_insert_node_generic(&vc4->hvs->lbm_mm,
> -                                                      &vc4_state->lbm,
> -                                                      lbm_size, 32, 0, 0);
> -                     spin_unlock_irqrestore(&vc4->hvs->mm_lock, irqflags);
> -             } else {
> -                     WARN_ON_ONCE(lbm_size != vc4_state->lbm.size);
> -             }
> -     }
>  
> +     ret = vc4_plane_setup_clipping_and_scaling(state);
>       if (ret)
>               return ret;
>  
> @@ -717,15 +735,18 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
>               vc4_dlist_write(vc4_state, SCALER_CSC2_ITR_R_601_5);
>       }
>  
> +     vc4_state->lbm_offset = 0;
> +
>       if (vc4_state->x_scaling[0] != VC4_SCALING_NONE ||
>           vc4_state->x_scaling[1] != VC4_SCALING_NONE ||
>           vc4_state->y_scaling[0] != VC4_SCALING_NONE ||
>           vc4_state->y_scaling[1] != VC4_SCALING_NONE) {
> -             /* LBM Base Address. */
> +             /* Reserve a slot for the LBM Base Address. The real value will
> +              * be set when calling vc4_plane_update_lbm().
> +              */
>               if (vc4_state->y_scaling[0] != VC4_SCALING_NONE ||
> -                 vc4_state->y_scaling[1] != VC4_SCALING_NONE) {
> -                     vc4_dlist_write(vc4_state, vc4_state->lbm.start);
> -             }
> +                 vc4_state->y_scaling[1] != VC4_SCALING_NONE)
> +                     vc4_state->lbm_offset = vc4_state->dlist_count++;
>  
>               if (num_planes > 1) {
>                       /* Emit Cb/Cr as channel 0 and Y as channel
> @@ -785,13 +806,18 @@ static int vc4_plane_atomic_check(struct drm_plane 
> *plane,
>                                 struct drm_plane_state *state)
>  {
>       struct vc4_plane_state *vc4_state = to_vc4_plane_state(state);
> +     int ret;
>  
>       vc4_state->dlist_count = 0;
>  
> -     if (plane_enabled(state))
> -             return vc4_plane_mode_set(plane, state);
> -     else
> +     if (!plane_enabled(state))
>               return 0;
> +
> +     ret = vc4_plane_mode_set(plane, state);
> +     if (ret)
> +             return ret;
> +
> +     return vc4_plane_update_lbm(state);
>  }

Couldn't you call update_lbm() (maybe called allocate_lbm()) first, and
then leave the dlist setup as is without needing lbm_offset?

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