[PATCH] drm: komeda: Fix an issue related to normalized zpos

[Liviu Dudau]

Hi Hongchi,

On Wed, Aug 21, 2024 at 04:56:13PM +0800, hongchi.peng wrote:
> We use komeda_crtc_normalize_zpos to normalize zpos of affected planes
> to their blending zorder in CU. If there's only one slave plane in
> affected planes and its layer_split property is enabled, order++ for
> its split layer, so that when calculating the normalized_zpos
> of master planes, the split layer of the slave plane is included, but
> the max_slave_zorder does not include the split layer and keep zero
> because there's only one slave plane in affacted planes, although we
> actually use two slave layers in this commit.
> 
> In most cases, this bug does not result in a commit failure, but assume
> the following situation:
>     slave_layer 0: zpos = 0, layer split enabled, normalized_zpos =
>     0;(use slave_layer 2 as its split layer)
>     master_layer 0: zpos = 2, layer_split enabled, normalized_zpos =
>     2;(use master_layer 2 as its split layer)
>     master_layer 1: zpos = 4, normalized_zpos = 4;
>     master_layer 3: zpos = 5, normalized_zpos = 5;
>     kcrtc_st->max_slave_zorder = 0;
> When we use master_layer 3 as a input of CU in function
> komeda_compiz_set_input and check it with function
> komeda_component_check_input, the parameter idx is equal to
> normailzed_zpos minus max_slave_zorder, the value of idx is 5
> and is euqal to CU's max_active_inputs, so that
> komeda_component_check_input returns a -EINVAL value.

Yes, indeed, you have found a bug in the calculations when layer_split is set.
But I was also looking through the code trying to find where layer_split gets
set and I could not find it, do you have some extra patches?

> 
> To fix the bug described above, when calculating the max_slave_zorder
> with the layer_split enabled, count the split layer in this calculation
> directly.
> 
> Signed-off-by: hongchi.peng <hongchi.peng at siengine.com>
> ---
>  drivers/gpu/drm/arm/display/komeda/komeda_kms.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> index fe46b0ebefea..b3db828284e4 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> @@ -159,7 +159,7 @@ static int komeda_crtc_normalize_zpos(struct drm_crtc *crtc,
>  	struct drm_plane_state *plane_st;
>  	struct drm_plane *plane;
>  	struct list_head zorder_list;
> -	int order = 0, err;
> +	int order = 0, slave_zpos, err;

Also, the build bot has already flagged it, your patch needs some improvements.
slave_zpos needs to be u32 if it's going to be compared against max_slave_zorder.

Best regards,
Liviu

>  
>  	DRM_DEBUG_ATOMIC("[CRTC:%d:%s] calculating normalized zpos values\n",
>  			 crtc->base.id, crtc->name);
> @@ -199,10 +199,13 @@ static int komeda_crtc_normalize_zpos(struct drm_crtc *crtc,
>  				 plane_st->zpos, plane_st->normalized_zpos);
>  
>  		/* calculate max slave zorder */
> -		if (has_bit(drm_plane_index(plane), kcrtc->slave_planes))
> +		if (has_bit(drm_plane_index(plane), kcrtc->slave_planes)) {
> +			slave_zpos = plane_st->normalized_zpos;
> +			if (to_kplane_st(plane_st)->layer_split)
> +				slave_zpos++;
>  			kcrtc_st->max_slave_zorder =
> -				max(plane_st->normalized_zpos,
> -				    kcrtc_st->max_slave_zorder);
> +				max(slave_zpos, kcrtc_st->max_slave_zorder);
> +		}
>  	}
>  
>  	crtc_st->zpos_changed = true;
> -- 
> 2.34.1
> 

-- 
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