drm/vkms: Map output framebuffer BOs with drm_gem_fb_vmap()

Abstract the framebuffer details by mappings its BOs with a call
to drm_gem_fb_vmap(). Unmap with drm_gem_fb_vunamp().

Before, the output address with stored as raw pointer in the priv
field of struct drm_writeback_job. Introduce the new type
struct vkms_writeback_job, which holds the output mappings addresses
while the writeback job is active.

The patchset also cleans up some internal casting an setup of the
output addresses. No functional changes.

v3:
	* free instances of struct vkms_writeback_job on cleanup
	  or errors
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730183511.20080-6-tzimmermann@suse.de

drivers/gpu/drm/vkms/vkms_composer.c

@@ -257,7 +257,7 @@ void vkms_composer_worker(struct work_struct *work)
 		return;
 
 	if (wb_pending)
-		vaddr_out = crtc_state->active_writeback;
+		vaddr_out = crtc_state->active_writeback->map[0].vaddr;
 
 	ret = compose_active_planes(&vaddr_out, primary_composer,
 				    crtc_state);

drivers/gpu/drm/vkms/vkms_drv.h

@@ -20,6 +20,10 @@
 #define XRES_MAX  8192
 #define YRES_MAX  8192
 
+struct vkms_writeback_job {
+	struct dma_buf_map map[DRM_FORMAT_MAX_PLANES];
+};
+
 struct vkms_composer {
 	struct drm_framebuffer fb;
 	struct drm_rect src, dst;
@@ -57,7 +61,7 @@ struct vkms_crtc_state {
 	int num_active_planes;
 	/* stack of active planes for crc computation, should be in z order */
 	struct vkms_plane_state **active_planes;
-	void *active_writeback;
+	struct vkms_writeback_job *active_writeback;
 
 	/* below four are protected by vkms_output.composer_lock */
 	bool crc_pending;

drivers/gpu/drm/vkms/vkms_writeback.c

@@ -65,41 +65,45 @@ static int vkms_wb_connector_get_modes(struct drm_connector *connector)
 static int vkms_wb_prepare_job(struct drm_writeback_connector *wb_connector,
 			       struct drm_writeback_job *job)
 {
-	struct drm_gem_object *gem_obj;
-	struct dma_buf_map map;
+	struct vkms_writeback_job *vkmsjob;
 	int ret;
 
 	if (!job->fb)
 		return 0;
 
-	gem_obj = drm_gem_fb_get_obj(job->fb, 0);
-	ret = drm_gem_shmem_vmap(gem_obj, &map);
+	vkmsjob = kzalloc(sizeof(*vkmsjob), GFP_KERNEL);
+	if (!vkmsjob)
+		return -ENOMEM;
+
+	ret = drm_gem_fb_vmap(job->fb, vkmsjob->map);
 	if (ret) {
 		DRM_ERROR("vmap failed: %d\n", ret);
-		return ret;
+		goto err_kfree;
 	}
 
-	job->priv = map.vaddr;
+	job->priv = vkmsjob;
 
 	return 0;
+
+err_kfree:
+	kfree(vkmsjob);
+	return ret;
 }
 
 static void vkms_wb_cleanup_job(struct drm_writeback_connector *connector,
 				struct drm_writeback_job *job)
 {
-	struct drm_gem_object *gem_obj;
+	struct vkms_writeback_job *vkmsjob = job->priv;
 	struct vkms_device *vkmsdev;
-	struct dma_buf_map map;
 
 	if (!job->fb)
 		return;
 
-	gem_obj = drm_gem_fb_get_obj(job->fb, 0);
-	dma_buf_map_set_vaddr(&map, job->priv);
-	drm_gem_shmem_vunmap(gem_obj, &map);
+	drm_gem_fb_vunmap(job->fb, vkmsjob->map);
 
-	vkmsdev = drm_device_to_vkms_device(gem_obj->dev);
+	vkmsdev = drm_device_to_vkms_device(job->fb->dev);
 	vkms_set_composer(&vkmsdev->output, false);
+	kfree(vkmsjob);
 }
 
 static void vkms_wb_atomic_commit(struct drm_connector *conn,