[PATCH v2 2/2] drm: ensure blend mode supported if alpha exposed

[Leandro Ribeiro <leandro.ribeiro@collabora.com>]

Before "drm/drm_blend: allow blend mode property without PREMULTI",
userspace would have to assume that only PREMULTI was supported by
drivers that didn't expose the blend mode property. But now userspace
shouldn't relly on that, as they can't count with drivers always
supporting PREMULTI.

Error out if a driver expose alpha property or pixel formats with alpha
and does not expose the blend mode property. This way userspace don't
have to guess. Drivers that hit such error must be fixed.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>
---
 drivers/gpu/drm/drm_crtc_internal.h |  1 +
 drivers/gpu/drm/drm_drv.c           |  7 ++++-
 drivers/gpu/drm/drm_mode_config.c   | 42 +++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
index c09409229644..bdbb6b9b94ea 100644
--- a/drivers/gpu/drm/drm_crtc_internal.h
+++ b/drivers/gpu/drm/drm_crtc_internal.h
@@ -96,6 +96,7 @@ int drm_mode_setcrtc(struct drm_device *dev,
 int drm_modeset_register_all(struct drm_device *dev);
 void drm_modeset_unregister_all(struct drm_device *dev);
 void drm_mode_config_validate(struct drm_device *dev);
+int drm_mode_config_enforce(struct drm_device *dev);
 
 /* drm_modes.c */
 const char *drm_get_mode_status_name(enum drm_mode_status status);
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 985c283cf59f..76766a370650 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -1059,9 +1059,14 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags)
 	const struct drm_driver *driver = dev->driver;
 	int ret;
 
-	if (!driver->load)
+	if (!driver->load) {
 		drm_mode_config_validate(dev);
 
+		ret = drm_mode_config_enforce(dev);
+		if (ret)
+			return ret;
+	}
+
 	WARN_ON(!dev->managed.final_kfree);
 
 	if (drm_dev_needs_global_mutex(dev))
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 66f7dc37b597..20fd26ecb957 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -738,3 +738,45 @@ void drm_mode_config_validate(struct drm_device *dev)
 	     "Must have as many primary planes as there are CRTCs, but have %u primary planes and %u CRTCs",
 	     num_primary, dev->mode_config.num_crtc);
 }
+
+static int plane_require_blend_mode_for_alpha(struct drm_plane *plane)
+{
+	struct drm_device *dev = plane->dev;
+	const struct drm_format_info *fmt;
+	u32 i;
+
+	/* blend mode property supported, no need to check anything */
+	if (plane->blend_mode_property)
+		return 0;
+
+	if (plane->alpha_property) {
+		drm_err(dev, "[PLANE:%d:%s] alpha property exposed but blend mode not setup",
+			plane->base.id, plane->name);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < plane->format_count; i++) {
+		fmt = drm_format_info(plane->format_types[i]);
+		if (fmt->has_alpha) {
+			drm_err(dev, "[PLANE:%d:%s] pixel format with alpha exposed but blend mode not setup",
+			        plane->base.id, plane->name);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+int drm_mode_config_enforce(struct drm_device *dev)
+{
+	struct drm_plane *plane;
+	int ret;
+
+	drm_for_each_plane(plane, dev) {
+		ret = plane_require_blend_mode_for_alpha(plane);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
-- 
2.54.0