drm/plane-helper: Add drm_plane_helper_check_update() (v3)

Pull the parameter checking from drm_primary_helper_update() out into
its own function; drivers that provide their own setplane()
implementations rather than using the helper may still want to share
this parameter checking logic.

A few of the checks here were also updated based on suggestions by
Ville Syrjälä.

v3:
 - s/primary_helper/plane_helper/ --- this checking logic may be useful
   for other types of planes as well.
 - Fix visibility check (need to dereference visibility pointer)
v2:
 - Pass src/dest/clip rects and min/max scaling down to helper to avoid
   duplication of effort between helper and drivers (suggested by
   Ville).
 - Allow caller to specify whether the primary plane should be
   updatable while the crtc is disabled.

Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Chon Ming Lee <chon.ming.lee@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
[danvet: Include header properly and fixup declaration mismatch to
make this compile.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_plane_helper.c

@@ -25,6 +25,7 @@
 
 #include <linux/list.h>
 #include <drm/drmP.h>
+#include <drm/drm_plane_helper.h>
 #include <drm/drm_rect.h>
 #include <drm/drm_plane_helper.h>
 
@@ -73,6 +74,79 @@ static int get_connectors_for_crtc(struct drm_crtc *crtc,
 	return count;
 }
 
+/**
+ * drm_plane_helper_check_update() - Check plane update for validity
+ * @plane: plane object to update
+ * @crtc: owning CRTC of owning plane
+ * @fb: framebuffer to flip onto plane
+ * @src: source coordinates in 16.16 fixed point
+ * @dest: integer destination coordinates
+ * @clip: integer clipping coordinates
+ * @min_scale: minimum @src:@dest scaling factor in 16.16 fixed point
+ * @max_scale: maximum @src:@dest scaling factor in 16.16 fixed point
+ * @can_position: is it legal to position the plane such that it
+ *                doesn't cover the entire crtc?  This will generally
+ *                only be false for primary planes.
+ * @can_update_disabled: can the plane be updated while the crtc
+ *                       is disabled?
+ * @visible: output parameter indicating whether plane is still visible after
+ *           clipping
+ *
+ * Checks that a desired plane update is valid.  Drivers that provide
+ * their own plane handling rather than helper-provided implementations may
+ * still wish to call this function to avoid duplication of error checking
+ * code.
+ *
+ * RETURNS:
+ * Zero if update appears valid, error code on failure
+ */
+int drm_plane_helper_check_update(struct drm_plane *plane,
+				    struct drm_crtc *crtc,
+				    struct drm_framebuffer *fb,
+				    struct drm_rect *src,
+				    struct drm_rect *dest,
+				    const struct drm_rect *clip,
+				    int min_scale,
+				    int max_scale,
+				    bool can_position,
+				    bool can_update_disabled,
+				    bool *visible)
+{
+	int hscale, vscale;
+
+	if (!crtc->enabled && !can_update_disabled) {
+		DRM_DEBUG_KMS("Cannot update plane of a disabled CRTC.\n");
+		return -EINVAL;
+	}
+
+	/* Check scaling */
+	hscale = drm_rect_calc_hscale(src, dest, min_scale, max_scale);
+	vscale = drm_rect_calc_vscale(src, dest, min_scale, max_scale);
+	if (hscale < 0 || vscale < 0) {
+		DRM_DEBUG_KMS("Invalid scaling of plane\n");
+		return -ERANGE;
+	}
+
+	*visible = drm_rect_clip_scaled(src, dest, clip, hscale, vscale);
+	if (!*visible)
+		/*
+		 * Plane isn't visible; some drivers can handle this
+		 * so we just return success here.  Drivers that can't
+		 * (including those that use the primary plane helper's
+		 * update function) will return an error from their
+		 * update_plane handler.
+		 */
+		return 0;
+
+	if (!can_position && !drm_rect_equals(dest, clip)) {
+		DRM_DEBUG_KMS("Plane must cover entire CRTC\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_plane_helper_check_update);
+
 /**
  * drm_primary_helper_update() - Helper for primary plane update
  * @plane: plane object to update
@@ -121,51 +195,42 @@ int drm_primary_helper_update(struct drm_plane *plane, struct drm_crtc *crtc,
 		.x = src_x >> 16,
 		.y = src_y >> 16,
 	};
+	struct drm_rect src = {
+		.x1 = src_x,
+		.y1 = src_y,
+		.x2 = src_x + src_w,
+		.y2 = src_y + src_h,
+	};
 	struct drm_rect dest = {
 		.x1 = crtc_x,
 		.y1 = crtc_y,
 		.x2 = crtc_x + crtc_w,
 		.y2 = crtc_y + crtc_h,
 	};
-	struct drm_rect clip = {
+	const struct drm_rect clip = {
 		.x2 = crtc->mode.hdisplay,
 		.y2 = crtc->mode.vdisplay,
 	};
 	struct drm_connector **connector_list;
 	int num_connectors, ret;
+	bool visible;
 
-	if (!crtc->enabled) {
-		DRM_DEBUG_KMS("Cannot update primary plane of a disabled CRTC.\n");
-		return -EINVAL;
-	}
-
-	/* Disallow subpixel positioning */
-	if ((src_x | src_y | src_w | src_h) & SUBPIXEL_MASK) {
-		DRM_DEBUG_KMS("Primary plane does not support subpixel positioning\n");
-		return -EINVAL;
-	}
-
-	/* Disallow scaling */
-	src_w >>= 16;
-	src_h >>= 16;
-	if (crtc_w != src_w || crtc_h != src_h) {
-		DRM_DEBUG_KMS("Can't scale primary plane\n");
-		return -EINVAL;
-	}
-
-	/* Make sure primary plane covers entire CRTC */
-	drm_rect_intersect(&dest, &clip);
-	if (dest.x1 != 0 || dest.y1 != 0 ||
-	    dest.x2 != crtc->mode.hdisplay || dest.y2 != crtc->mode.vdisplay) {
-		DRM_DEBUG_KMS("Primary plane must cover entire CRTC\n");
-		return -EINVAL;
-	}
-
-	/* Framebuffer must be big enough to cover entire plane */
-	ret = drm_crtc_check_viewport(crtc, crtc_x, crtc_y, &crtc->mode, fb);
+	ret = drm_plane_helper_check_update(plane, crtc, fb,
+					    &src, &dest, &clip,
+					    DRM_PLANE_HELPER_NO_SCALING,
+					    DRM_PLANE_HELPER_NO_SCALING,
+					    false, false, &visible);
 	if (ret)
 		return ret;
 
+	if (!visible)
+		/*
+		 * Primary plane isn't visible.  Note that unless a driver
+		 * provides their own disable function, this will just
+		 * wind up returning -EINVAL to userspace.
+		 */
+		return plane->funcs->disable_plane(plane);
+
 	/* Find current connectors for CRTC */
 	num_connectors = get_connectors_for_crtc(crtc, NULL, 0);
 	BUG_ON(num_connectors == 0);

include/drm/drm_plane_helper.h

@@ -24,13 +24,35 @@
 #ifndef DRM_PLANE_HELPER_H
 #define DRM_PLANE_HELPER_H
 
+#include <drm/drm_rect.h>
+
+/*
+ * Drivers that don't allow primary plane scaling may pass this macro in place
+ * of the min/max scale parameters of the update checker function.
+ *
+ * Due to src being in 16.16 fixed point and dest being in integer pixels,
+ * 1<<16 represents no scaling.
+ */
+#define DRM_PLANE_HELPER_NO_SCALING (1<<16)
+
 /**
  * DOC: plane helpers
  *
  * Helper functions to assist with creation and handling of CRTC primary
  * planes.
  */
 
+extern int drm_plane_helper_check_update(struct drm_plane *plane,
+					 struct drm_crtc *crtc,
+					 struct drm_framebuffer *fb,
+					 struct drm_rect *src,
+					 struct drm_rect *dest,
+					 const struct drm_rect *clip,
+					 int min_scale,
+					 int max_scale,
+					 bool can_position,
+					 bool can_update_disabled,
+					 bool *visible);
 extern int drm_primary_helper_update(struct drm_plane *plane,
 				     struct drm_crtc *crtc,
 				     struct drm_framebuffer *fb,