Re: [Freedreno] [PATCH v2 16/22] drm/msm/dpu: do not limit the zpos property

[abhinavk@codeaurora.org]

On 2021-07-04 18:21, Dmitry Baryshkov wrote:
> Stop limiting zpos property values, we use normalized_zpos anyway. And
> nothing stops userspace from assigning several planes to a single zpos
> (it is a userspace bug, but the kernel is forgiving about it).

Userspace assigning several planes to a single zpos was intended to 
identify
cases where src split can be used. Downstream does not use normalized 
zpos,
hence it did not come across as a bug but mostly as a way to identify 
when
usermode needs src split to be enabled based on the composition 
strategy.

We can talk about that more in the rest of the patches of this series.

For this one, I only have a couple of questions:

1) Across different vendors, some have gone with limiting the zpos and 
some have gone with
the max, so is there an issue with sticking with the max_blend_stages 
limit?

2) If there is no hard reason to make this change, I think its better to 
keep it the way it is.

> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> index 8ed7b8f0db69..3850f2714bf3 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> @@ -44,7 +44,6 @@
>  #define DPU_NAME_SIZE  12
> 
>  #define DPU_PLANE_COLOR_FILL_FLAG	BIT(31)
> -#define DPU_ZPOS_MAX 255
> 
>  /* multirect rect index */
>  enum {
> @@ -1374,7 +1373,6 @@ struct drm_plane *dpu_plane_init(struct 
> drm_device *dev,
>  	struct dpu_plane *pdpu;
>  	struct msm_drm_private *priv = dev->dev_private;
>  	struct dpu_kms *kms = to_dpu_kms(priv->kms);
> -	int zpos_max = DPU_ZPOS_MAX;
>  	uint32_t num_formats;
>  	int ret = -EINVAL;
> 
> @@ -1412,14 +1410,7 @@ struct drm_plane *dpu_plane_init(struct 
> drm_device *dev,
> 
>  	pdpu->catalog = kms->catalog;
> 
> -	if (kms->catalog->mixer_count &&
> -		kms->catalog->mixer[0].sblk->maxblendstages) {
> -		zpos_max = kms->catalog->mixer[0].sblk->maxblendstages - 1;
> -		if (zpos_max > DPU_STAGE_MAX - DPU_STAGE_0 - 1)
> -			zpos_max = DPU_STAGE_MAX - DPU_STAGE_0 - 1;
> -	}
> -
> -	ret = drm_plane_create_zpos_property(plane, 0, 0, zpos_max);
> +	ret = drm_plane_create_zpos_property(plane, 0, 0, 255);
>  	if (ret)
>  		DPU_ERROR("failed to install zpos property, rc = %d\n", ret);