drm/fb-helper: implement ioctl FBIO_WAITFORVSYNC

Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
framebuffer emulation driver. Legacy framebuffer users like non kms/drm
based OpenGL(ES)/EGL implementations may require the ioctl to
synchronize drawing or buffer flip for double buffering. It is tested on
the i.MX6.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_fb_helper.c

@@ -1244,6 +1244,74 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
 }
 EXPORT_SYMBOL(drm_fb_helper_setcmap);
 
+/**
+ * drm_fb_helper_ioctl - legacy ioctl implementation
+ * @info: fbdev registered by the helper
+ * @cmd: ioctl command
+ * @arg: ioctl argument
+ *
+ * A helper to implement the standard fbdev ioctl. Only
+ * FBIO_WAITFORVSYNC is implemented for now.
+ */
+int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
+			unsigned long arg)
+{
+	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_device *dev = fb_helper->dev;
+	struct drm_mode_set *mode_set;
+	struct drm_crtc *crtc;
+	int ret = 0;
+
+	mutex_lock(&dev->mode_config.mutex);
+	if (!drm_fb_helper_is_bound(fb_helper)) {
+		ret = -EBUSY;
+		goto unlock;
+	}
+
+	switch (cmd) {
+	case FBIO_WAITFORVSYNC:
+		/*
+		 * Only consider the first CRTC.
+		 *
+		 * This ioctl is supposed to take the CRTC number as
+		 * an argument, but in fbdev times, what that number
+		 * was supposed to be was quite unclear, different
+		 * drivers were passing that argument differently
+		 * (some by reference, some by value), and most of the
+		 * userspace applications were just hardcoding 0 as an
+		 * argument.
+		 *
+		 * The first CRTC should be the integrated panel on
+		 * most drivers, so this is the best choice we can
+		 * make. If we're not smart enough here, one should
+		 * just consider switch the userspace to KMS.
+		 */
+		mode_set = &fb_helper->crtc_info[0].mode_set;
+		crtc = mode_set->crtc;
+
+		/*
+		 * Only wait for a vblank event if the CRTC is
+		 * enabled, otherwise just don't do anythintg,
+		 * not even report an error.
+		 */
+		ret = drm_crtc_vblank_get(crtc);
+		if (!ret) {
+			drm_crtc_wait_one_vblank(crtc);
+			drm_crtc_vblank_put(crtc);
+		}
+
+		ret = 0;
+		goto unlock;
+	default:
+		ret = -ENOTTY;
+	}
+
+unlock:
+	mutex_unlock(&dev->mode_config.mutex);
+	return ret;
+}
+EXPORT_SYMBOL(drm_fb_helper_ioctl);
+
 /**
  * drm_fb_helper_check_var - implementation for &fb_ops.fb_check_var
  * @var: screeninfo to check

include/drm/drm_fb_helper.h

@@ -230,7 +230,8 @@ struct drm_fb_helper {
 	.fb_blank	= drm_fb_helper_blank, \
 	.fb_pan_display	= drm_fb_helper_pan_display, \
 	.fb_debug_enter = drm_fb_helper_debug_enter, \
-	.fb_debug_leave = drm_fb_helper_debug_leave
+	.fb_debug_leave = drm_fb_helper_debug_leave, \
+	.fb_ioctl	= drm_fb_helper_ioctl
 
 #ifdef CONFIG_DRM_FBDEV_EMULATION
 void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
@@ -284,6 +285,9 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
 
 int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
 
+int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
+			unsigned long arg);
+
 int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
 int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
 int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
@@ -371,6 +375,12 @@ static inline int drm_fb_helper_setcmap(struct fb_cmap *cmap,
 	return 0;
 }
 
+static inline int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
+				      unsigned long arg)
+{
+	return 0;
+}
+
 static inline void drm_fb_helper_unlink_fbi(struct drm_fb_helper *fb_helper)
 {
 }