Modern compositor rely on zpos management to offload some processing to
deticated hardware. In order to test multiple configurations, add zpos
configuration to configFS.

Introduce multiple attributes to configure zpos:
- zpos_enabled - Create or not the zpos property. If not created, the zpos
  is undefined.
- zpos_mutable - If the zpos property is created, allow or not the
  userspace to modify it
- zpos_initial - Initial value for zpos property. Must be between zpos_min
  and zpos_max
- zpos_min - Minimum zpos value for this plane. Must be <= zpos_max
- zpos_max - Maximum zpos value for this plane. Must be >= zpos_min

Reviewed-by: Luca Ceresoli <[email protected]>
Signed-off-by: Louis Chauvet <[email protected]>
---
 Documentation/ABI/testing/configfs-vkms |  36 +++++++
 Documentation/gpu/vkms.rst              |   9 +-
 drivers/gpu/drm/vkms/vkms_configfs.c    | 180 ++++++++++++++++++++++++++++++++
 3 files changed, 224 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/configfs-vkms 
b/Documentation/ABI/testing/configfs-vkms
index 48f92538c602..34cb6aeec411 100644
--- a/Documentation/ABI/testing/configfs-vkms
+++ b/Documentation/ABI/testing/configfs-vkms
@@ -162,6 +162,42 @@ Description:
         use '-' prefix. Use '+*' to add all formats, '-*' to
         remove all.
 
+What:          /sys/kernel/config/vkms/<device>/planes/<plane>/zpos_enabled
+Date:          Nov 2025
+Contact:       [email protected]
+Description:
+        Enable or disable the zpos property. Value: 1 - enabled,
+        0 - disabled.
+
+What:          /sys/kernel/config/vkms/<device>/planes/<plane>/zpos_mutable
+Date:          Nov 2025
+Contact:       [email protected]
+Description:
+        Create the zpos property as mutable or immutable.
+        Value: 1 - mutable, 0 - immutable. No effect if
+        zpos_enabled is not set.
+
+What:          /sys/kernel/config/vkms/<device>/planes/<plane>/zpos_initial
+Date:          Nov 2025
+Contact:       [email protected]
+Description:
+        Set the initial zpos value. Must be between zpos_min
+        and zpos_max. No effect if zpos_enabled is not set.
+
+What:          /sys/kernel/config/vkms/<device>/planes/<plane>/zpos_min
+Date:          Nov 2025
+Contact:       [email protected]
+Description:
+        Set the minimal zpos value. No effect if zpos_enabled
+        is not set.
+
+What:          /sys/kernel/config/vkms/<device>/planes/<plane>/zpos_max
+Date:          Nov 2025
+Contact:       [email protected]
+Description:
+        Set the maximal zpos value. No effect if zpos_enabled
+        is not set.
+
 What:          /sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
 Date:          Nov 2025
 Contact:       [email protected]
diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index 15d62ad963c9..791c4f33a90a 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -87,7 +87,7 @@ Start by creating one or more planes::
 
   sudo mkdir /config/vkms/my-vkms/planes/plane0
 
-Planes have 9 configurable attributes:
+Planes have 14 configurable attributes:
 
 - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
   exposed by the "type" property of a plane)
@@ -114,6 +114,13 @@ Planes have 9 configurable attributes:
   To remove a format, use a minus and its fourcc: -XR24
   To add all formats use +*
   To remove all formats, use -*
+- zpos_enabled: Enable or not the zpos property: 1 enable, 0 disable
+- zpos_mutable: Create the zpos property as a mutable or imutable property: 1 
mutable,
+  0 immutable. No effect if zpos_enabled is not set.
+- zpos_initial: Set the initial zpos value. Must be between zpos_min and 
zpos_max. No
+  effect if zpos_enabled is not set.
+- zpos_min: Set the minimum zpos value. No effect if zpos_enabled is not set.
+- zpos_max: Set the maximum zpos value. No effect if zpos_enabled is not set.
 
 Continue by creating one or more CRTCs::
 
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c 
b/drivers/gpu/drm/vkms/vkms_configfs.c
index a451d1122acf..e7f3ab54b5a1 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -744,6 +744,176 @@ static ssize_t plane_supported_formats_store(struct 
config_item *item,
        return count;
 }
 
+static ssize_t plane_zpos_enabled_show(struct config_item *item, char *page)
+{
+       struct vkms_configfs_plane *plane;
+       bool enabled;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       scoped_guard(mutex, &plane->dev->lock)
+               enabled = vkms_config_plane_get_zpos_enabled(plane->config);
+
+       return sprintf(page, "%d\n", enabled);
+}
+
+static ssize_t plane_zpos_enabled_store(struct config_item *item, const char 
*page,
+                                       size_t count)
+{
+       struct vkms_configfs_plane *plane;
+       bool enabled;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       if (kstrtobool(page, &enabled))
+               return -EINVAL;
+
+       scoped_guard(mutex, &plane->dev->lock) {
+               if (plane->dev->enabled)
+                       return -EBUSY;
+
+               vkms_config_plane_set_zpos_enabled(plane->config, enabled);
+       }
+
+       return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_mutable_show(struct config_item *item, char *page)
+{
+       struct vkms_configfs_plane *plane;
+       bool mutable;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       scoped_guard(mutex, &plane->dev->lock)
+               mutable = vkms_config_plane_get_zpos_mutable(plane->config);
+
+       return sprintf(page, "%d\n", mutable);
+}
+
+static ssize_t plane_zpos_mutable_store(struct config_item *item, const char 
*page,
+                                       size_t count)
+{
+       struct vkms_configfs_plane *plane;
+       bool mutable;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       if (kstrtobool(page, &mutable))
+               return -EINVAL;
+
+       scoped_guard(mutex, &plane->dev->lock) {
+               if (plane->dev->enabled)
+                       return -EBUSY;
+
+               vkms_config_plane_set_zpos_mutable(plane->config, mutable);
+       }
+
+       return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_initial_show(struct config_item *item, char *page)
+{
+       struct vkms_configfs_plane *plane;
+       unsigned int initial;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       scoped_guard(mutex, &plane->dev->lock)
+               initial = vkms_config_plane_get_zpos_initial(plane->config);
+
+       return sprintf(page, "%u\n", initial);
+}
+
+static ssize_t plane_zpos_initial_store(struct config_item *item, const char 
*page,
+                                       size_t count)
+{
+       struct vkms_configfs_plane *plane;
+       unsigned int initial;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       if (kstrtouint(page, 10, &initial))
+               return -EINVAL;
+
+       scoped_guard(mutex, &plane->dev->lock) {
+               if (plane->dev->enabled)
+                       return -EBUSY;
+
+               vkms_config_plane_set_zpos_initial(plane->config, initial);
+       }
+
+       return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_min_show(struct config_item *item, char *page)
+{
+       struct vkms_configfs_plane *plane;
+       unsigned int min;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       scoped_guard(mutex, &plane->dev->lock)
+               min = vkms_config_plane_get_zpos_min(plane->config);
+
+       return sprintf(page, "%u\n", min);
+}
+
+static ssize_t plane_zpos_min_store(struct config_item *item, const char *page,
+                                   size_t count)
+{
+       struct vkms_configfs_plane *plane;
+       unsigned int min;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       if (kstrtouint(page, 10, &min))
+               return -EINVAL;
+
+       scoped_guard(mutex, &plane->dev->lock) {
+               if (plane->dev->enabled)
+                       return -EBUSY;
+
+               vkms_config_plane_set_zpos_min(plane->config, min);
+       }
+
+       return (ssize_t)count;
+}
+
+static ssize_t plane_zpos_max_show(struct config_item *item, char *page)
+{
+       struct vkms_configfs_plane *plane;
+       unsigned int max;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       scoped_guard(mutex, &plane->dev->lock)
+               max = vkms_config_plane_get_zpos_max(plane->config);
+
+       return sprintf(page, "%u\n", max);
+}
+
+static ssize_t plane_zpos_max_store(struct config_item *item, const char *page,
+                                   size_t count)
+{
+       struct vkms_configfs_plane *plane;
+       unsigned int max;
+
+       plane = plane_item_to_vkms_configfs_plane(item);
+
+       if (kstrtouint(page, 10, &max))
+               return -EINVAL;
+
+       scoped_guard(mutex, &plane->dev->lock) {
+               if (plane->dev->enabled)
+                       return -EBUSY;
+
+               vkms_config_plane_set_zpos_max(plane->config, max);
+       }
+
+       return (ssize_t)count;
+}
+
 CONFIGFS_ATTR(plane_, type);
 CONFIGFS_ATTR(plane_, name);
 CONFIGFS_ATTR(plane_, supported_rotations);
@@ -753,6 +923,11 @@ CONFIGFS_ATTR(plane_, default_color_range);
 CONFIGFS_ATTR(plane_, supported_color_encodings);
 CONFIGFS_ATTR(plane_, default_color_encoding);
 CONFIGFS_ATTR(plane_, supported_formats);
+CONFIGFS_ATTR(plane_, zpos_enabled);
+CONFIGFS_ATTR(plane_, zpos_mutable);
+CONFIGFS_ATTR(plane_, zpos_initial);
+CONFIGFS_ATTR(plane_, zpos_min);
+CONFIGFS_ATTR(plane_, zpos_max);
 
 static struct configfs_attribute *plane_item_attrs[] = {
        &plane_attr_type,
@@ -764,6 +939,11 @@ static struct configfs_attribute *plane_item_attrs[] = {
        &plane_attr_supported_color_encodings,
        &plane_attr_default_color_encoding,
        &plane_attr_supported_formats,
+       &plane_attr_zpos_enabled,
+       &plane_attr_zpos_mutable,
+       &plane_attr_zpos_initial,
+       &plane_attr_zpos_min,
+       &plane_attr_zpos_max,
        NULL,
 };
 

-- 
2.51.2

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