[RFC v3 08/12] drm/framebuffer: Add drm_mode_can_dirtyfb()

["Noralf Trønnes" <noralf@tronnes.org>]

Add a function so the generic fbdev client can check if the framebuffer
does flushing. This is needed to set up deferred I/O.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
---
 drivers/gpu/drm/drm_framebuffer.c | 31 +++++++++++++++++++++++++++++++
 include/drm/drm_framebuffer.h     |  2 ++
 2 files changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/drm_framebuffer.c b/drivers/gpu/drm/drm_framebuffer.c
index ad8f7d308656..a659cff45844 100644
--- a/drivers/gpu/drm/drm_framebuffer.c
+++ b/drivers/gpu/drm/drm_framebuffer.c
@@ -600,6 +600,37 @@ int drm_mode_dirtyfb_ioctl(struct drm_device *dev,
 	return drm_mode_dirtyfb(dev, data, file_priv, true);
 }
 
+/**
+ * drm_mode_can_dirtyfb - check if the FB does flushing
+ * @dev: drm device
+ * @fb_id: Framebuffer id
+ * @file_priv: drm file
+ *
+ * Returns:
+ * True if the framebuffer does flushing, false otherwise.
+ */
+bool drm_mode_can_dirtyfb(struct drm_device *dev, u32 fb_id,
+			  struct drm_file *file_priv)
+{
+	struct drm_framebuffer *fb;
+	bool ret = false;
+
+	if (!drm_core_check_feature(dev, DRIVER_MODESET))
+		return false;
+
+	fb = drm_framebuffer_lookup(dev, file_priv, fb_id);
+	if (!fb)
+		return false;
+
+	if (fb->funcs->dirty)
+		ret = true;
+
+	drm_framebuffer_put(fb);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_mode_can_dirtyfb);
+
 /**
  * drm_fb_release - remove and free the FBs on this file
  * @priv: drm file for the ioctl
diff --git a/include/drm/drm_framebuffer.h b/include/drm/drm_framebuffer.h
index c50502c656e5..05d170f4e215 100644
--- a/include/drm/drm_framebuffer.h
+++ b/include/drm/drm_framebuffer.h
@@ -216,6 +216,8 @@ struct drm_framebuffer *drm_framebuffer_lookup(struct drm_device *dev,
 void drm_framebuffer_remove(struct drm_framebuffer *fb);
 void drm_framebuffer_cleanup(struct drm_framebuffer *fb);
 void drm_framebuffer_unregister_private(struct drm_framebuffer *fb);
+bool drm_mode_can_dirtyfb(struct drm_device *dev, u32 fb_id,
+			  struct drm_file *file_priv);
 
 /**
  * drm_framebuffer_get - acquire a framebuffer reference
-- 
2.15.1

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