qxl: refactor to use drm_fb_helper_fbdev_setup

Lots of code can be removed by relying on fb-helper:
- "struct drm_framebuffer" moves to fb_helper.fb.
- "struct drm_gem_object" moves to fb_helper.obj[0].
- "struct qxl_device" can be inferred as drm_fb_helper is embedded.
- qxl_user_framebuffer_create -> drm_gem_fb_create.
- qxl_user_framebuffer_destroy -> drm_gem_fb_destroy.
- qxl_fbdev_destroy -> drm_fb_helper_fbdev_teardown + vfree(shadow).

Remove unused code:
- qxl_fbdev_qobj_is_fb, qxl_fbdev_set_suspend.
- Unused fields of qxl_fbdev: delayed_ops, delayed_ops_lock, size.

Misc notes:
- The dirty callback is preserved as it is necessary to trigger update
  commands in the hw (the screen stays black otherwise).
- No idea when .create_handle in drm_framebuffer_funcs is used, but use
  the same drm_gem_fb_create_handle to match drm_gem_fb_funcs.
- I don't know why qxl_fb_find_or_create_single used to check for an
  existing framebuffer and removed that check to match other drivers.
- Use of drm_fb_helper_fbdev_teardown also requires "info->fbdefio" to
  be dynamically allocated. Replace the existing defio config by
  drm_fb_helper_defio_init to accomodate this.

Testing results: startx with fbdev, modesetting and qxl all seems to
work. Tested also with CONFIG_DRM_FBDEV_EMULATION=n, fbdev obviously
fails but others are fine. QEMU -spice and QEMU -spice with vdagent and
multiple (resized) displays (via remote-viewer) also works.
unbind vtconsole and rmmod has *not* regressed (i.e. it still trips on a
use-after-free in qxl_check_idle via qxl_ttm_fini).

Ideally setup/teardown is replaced by drm_fbdev_generic_setup as that
would result in further code reduction, improve error handling (like not
leaking shadow memory), but unfortunately QXL has no implementation for
qxl_gem_prime_vmap.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Link: http://patchwork.freedesktop.org/patch/msgid/20180910132156.23201-1-peter@lekensteyn.nl
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/qxl/qxl_drv.h

@@ -38,6 +38,7 @@
 
 #include <drm/drm_crtc.h>
 #include <drm/drm_encoder.h>
+#include <drm/drm_fb_helper.h>
 #include <drm/drm_gem.h>
 #include <drm/drmP.h>
 #include <drm/ttm/ttm_bo_api.h>
@@ -121,15 +122,9 @@ struct qxl_output {
 	struct drm_encoder enc;
 };
 
-struct qxl_framebuffer {
-	struct drm_framebuffer base;
-	struct drm_gem_object *obj;
-};
-
 #define to_qxl_crtc(x) container_of(x, struct qxl_crtc, base)
 #define drm_connector_to_qxl_output(x) container_of(x, struct qxl_output, base)
 #define drm_encoder_to_qxl_output(x) container_of(x, struct qxl_output, enc)
-#define to_qxl_framebuffer(x) container_of(x, struct qxl_framebuffer, base)
 
 struct qxl_mman {
 	struct ttm_bo_global_ref        bo_global_ref;
@@ -138,13 +133,6 @@ struct qxl_mman {
 	struct ttm_bo_device		bdev;
 };
 
-struct qxl_mode_info {
-	bool mode_config_initialized;
-
-	/* pointer to fbdev info structure */
-	struct qxl_fbdev *qfbdev;
-};
-
 
 struct qxl_memslot {
 	uint8_t		generation;
@@ -232,10 +220,9 @@ struct qxl_device {
 	void *ram;
 	struct qxl_mman		mman;
 	struct qxl_gem		gem;
-	struct qxl_mode_info mode_info;
 
-	struct fb_info			*fbdev_info;
-	struct qxl_framebuffer	*fbdev_qfb;
+	struct drm_fb_helper	fb_helper;
+
 	void *ram_physical;
 
 	struct qxl_ring *release_ring;
@@ -349,19 +336,8 @@ qxl_bo_physical_address(struct qxl_device *qdev, struct qxl_bo *bo,
 
 int qxl_fbdev_init(struct qxl_device *qdev);
 void qxl_fbdev_fini(struct qxl_device *qdev);
-int qxl_get_handle_for_primary_fb(struct qxl_device *qdev,
-				  struct drm_file *file_priv,
-				  uint32_t *handle);
-void qxl_fbdev_set_suspend(struct qxl_device *qdev, int state);
 
 /* qxl_display.c */
-void qxl_user_framebuffer_destroy(struct drm_framebuffer *fb);
-int
-qxl_framebuffer_init(struct drm_device *dev,
-		     struct qxl_framebuffer *rfb,
-		     const struct drm_mode_fb_cmd2 *mode_cmd,
-		     struct drm_gem_object *obj,
-		     const struct drm_framebuffer_funcs *funcs);
 void qxl_display_read_client_monitors_config(struct qxl_device *qdev);
 int qxl_create_monitors_object(struct qxl_device *qdev);
 int qxl_destroy_monitors_object(struct qxl_device *qdev);
@@ -471,7 +447,7 @@ void qxl_draw_opaque_fb(const struct qxl_fb_image *qxl_fb_image,
 			int stride /* filled in if 0 */);
 
 void qxl_draw_dirty_fb(struct qxl_device *qdev,
-		       struct qxl_framebuffer *qxl_fb,
+		       struct drm_framebuffer *fb,
 		       struct qxl_bo *bo,
 		       unsigned flags, unsigned color,
 		       struct drm_clip_rect *clips,