[PATCH] drm/tegra: Add zpos property for cursor planes

[PATCH] drm/tegra: Add zpos property for cursor planes

[Thierry Reding]

From: Thierry Reding <treding@nvidia.com>

As of commit 4dc55525b095 ("drm: plane: Verify that no or all planes
have a zpos property") a warning is emitted if there's a mix of planes
with and without a zpos property.

On Tegra, cursor planes are always composited on top of all other
planes, which is why they never had a zpos property attached to them.
However, since the composition order is fixed, this is trivial to
remedy by simply attaching an immutable zpos property to them.

Reported-by: Jonathan Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
---
 drivers/gpu/drm/tegra/dc.c  | 10 ++++++++--
 drivers/gpu/drm/tegra/hub.c |  2 +-
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
index 83f31c6e891c..e7a6eb952ece 100644
--- a/drivers/gpu/drm/tegra/dc.c
+++ b/drivers/gpu/drm/tegra/dc.c
@@ -787,7 +787,7 @@ static struct drm_plane *tegra_primary_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
-	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
+	drm_plane_create_zpos_property(&plane->base, 1 + plane->index, 1, 255);
 
 	err = drm_plane_create_rotation_property(&plane->base,
 						 DRM_MODE_ROTATE_0,
@@ -957,6 +957,7 @@ static struct drm_plane *tegra_dc_cursor_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(&plane->base, &tegra_cursor_plane_helper_funcs);
+	drm_plane_create_zpos_immutable_property(&plane->base, 0);
 
 	return &plane->base;
 }
@@ -1074,7 +1075,12 @@ static struct drm_plane *tegra_dc_overlay_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
-	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
+
+	if (!cursor)
+		drm_plane_create_zpos_property(&plane->base, 1 + plane->index,
+					       1, 255);
+	else
+		drm_plane_create_zpos_immutable_property(&plane->base, 0);
 
 	err = drm_plane_create_rotation_property(&plane->base,
 						 DRM_MODE_ROTATE_0,
diff --git a/drivers/gpu/drm/tegra/hub.c b/drivers/gpu/drm/tegra/hub.c
index a2ef8f218d4e..697d75bbb9fa 100644
--- a/drivers/gpu/drm/tegra/hub.c
+++ b/drivers/gpu/drm/tegra/hub.c
@@ -590,7 +590,7 @@ struct drm_plane *tegra_shared_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(p, &tegra_shared_plane_helper_funcs);
-	drm_plane_create_zpos_property(p, 0, 0, 255);
+	drm_plane_create_zpos_property(p, 1 + index, 1, 255);
 
 	return p;
 }
-- 
2.24.1

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Re: [PATCH] drm/tegra: Add zpos property for cursor planes

[Ville Syrjälä]

On Wed, Jun 10, 2020 at 01:30:59PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> As of commit 4dc55525b095 ("drm: plane: Verify that no or all planes
> have a zpos property") a warning is emitted if there's a mix of planes
> with and without a zpos property.
> 
> On Tegra, cursor planes are always composited on top of all other
> planes, which is why they never had a zpos property attached to them.
> However, since the composition order is fixed, this is trivial to
> remedy by simply attaching an immutable zpos property to them.
> 
> Reported-by: Jonathan Hunter <jonathanh@nvidia.com>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/gpu/drm/tegra/dc.c  | 10 ++++++++--
>  drivers/gpu/drm/tegra/hub.c |  2 +-
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index 83f31c6e891c..e7a6eb952ece 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -787,7 +787,7 @@ static struct drm_plane *tegra_primary_plane_create(struct drm_device *drm,
>  	}
>  
>  	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
> -	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
> +	drm_plane_create_zpos_property(&plane->base, 1 + plane->index, 1, 255);
>  
>  	err = drm_plane_create_rotation_property(&plane->base,
>  						 DRM_MODE_ROTATE_0,
> @@ -957,6 +957,7 @@ static struct drm_plane *tegra_dc_cursor_plane_create(struct drm_device *drm,
>  	}
>  
>  	drm_plane_helper_add(&plane->base, &tegra_cursor_plane_helper_funcs);
> +	drm_plane_create_zpos_immutable_property(&plane->base, 0);

zpos==0 means the plane is at the bottom of the pile. Doesn't seem to
agree what you say in the commit msg.

>  
>  	return &plane->base;
>  }
> @@ -1074,7 +1075,12 @@ static struct drm_plane *tegra_dc_overlay_plane_create(struct drm_device *drm,
>  	}
>  
>  	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
> -	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
> +
> +	if (!cursor)
> +		drm_plane_create_zpos_property(&plane->base, 1 + plane->index,
> +					       1, 255);
> +	else
> +		drm_plane_create_zpos_immutable_property(&plane->base, 0);
>  
>  	err = drm_plane_create_rotation_property(&plane->base,
>  						 DRM_MODE_ROTATE_0,
> diff --git a/drivers/gpu/drm/tegra/hub.c b/drivers/gpu/drm/tegra/hub.c
> index a2ef8f218d4e..697d75bbb9fa 100644
> --- a/drivers/gpu/drm/tegra/hub.c
> +++ b/drivers/gpu/drm/tegra/hub.c
> @@ -590,7 +590,7 @@ struct drm_plane *tegra_shared_plane_create(struct drm_device *drm,
>  	}
>  
>  	drm_plane_helper_add(p, &tegra_shared_plane_helper_funcs);
> -	drm_plane_create_zpos_property(p, 0, 0, 255);
> +	drm_plane_create_zpos_property(p, 1 + index, 1, 255);
>  
>  	return p;
>  }
> -- 
> 2.24.1
> 
> _______________________________________________
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> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel
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Re: [PATCH] drm/tegra: Add zpos property for cursor planes

[Dmitry Osipenko]

10.06.2020 14:30, Thierry Reding пишет:
> From: Thierry Reding <treding@nvidia.com>
> 
> As of commit 4dc55525b095 ("drm: plane: Verify that no or all planes
> have a zpos property") a warning is emitted if there's a mix of planes
> with and without a zpos property.
> 
> On Tegra, cursor planes are always composited on top of all other
> planes, which is why they never had a zpos property attached to them.
> However, since the composition order is fixed, this is trivial to
> remedy by simply attaching an immutable zpos property to them.
> 
> Reported-by: Jonathan Hunter <jonathanh@nvidia.com>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---

What problem does it solve?

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Re: [PATCH] drm/tegra: Add zpos property for cursor planes

[Daniel Stone]

Hi Dmitry,

On Thu, 11 Jun 2020 at 08:54, Dmitry Osipenko <digetx@gmail.com> wrote:
> 10.06.2020 14:30, Thierry Reding пишет:
> > From: Thierry Reding <treding@nvidia.com>
> > As of commit 4dc55525b095 ("drm: plane: Verify that no or all planes
> > have a zpos property") a warning is emitted if there's a mix of planes
> > with and without a zpos property.
>
> What problem does it solve?

Well, it fixes the WARN_ON, which asserts that either no planes have
the zpos property attached, or all planes have the zpos property
attached. When only _some_ planes have the property, the property is
pretty much useless: zpos exists to guarantee to userspace the
relative ordering between planes, defined by the value of the
property. If not all planes have the property, then userspace cannot
reason about the ordering, since some of the planes have undefined
ordering.

Cheers,
Daniel
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Re: [PATCH] drm/tegra: Add zpos property for cursor planes

[Dmitry Osipenko]

11.06.2020 11:17, Daniel Stone пишет:
> Hi Dmitry,
> 
> On Thu, 11 Jun 2020 at 08:54, Dmitry Osipenko <digetx@gmail.com> wrote:
>> 10.06.2020 14:30, Thierry Reding пишет:
>>> From: Thierry Reding <treding@nvidia.com>
>>> As of commit 4dc55525b095 ("drm: plane: Verify that no or all planes
>>> have a zpos property") a warning is emitted if there's a mix of planes
>>> with and without a zpos property.
>>
>> What problem does it solve?
> 
> Well, it fixes the WARN_ON, which asserts that either no planes have
> the zpos property attached, or all planes have the zpos property
> attached. When only _some_ planes have the property, the property is
> pretty much useless: zpos exists to guarantee to userspace the
> relative ordering between planes, defined by the value of the
> property. If not all planes have the property, then userspace cannot
> reason about the ordering, since some of the planes have undefined
> ordering.

Hello Daniel,

So it's a kernel warning, thank you for the clarification! I'm running
only older Tegras that have a black-n-white cursor plane, but this is
not supported by the upstream kernel. No wonder that I haven't seen the
warning, this made me curious what this patch is about :)
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