drm/vkms: Decouple crc operations from composer

In the vkms_composer.c, some of the functions related to CRC and compose
have interdependence between each other. This patch reworks some
functions inside vkms_composer to make crc and composer computation
decoupled.

This patch is preparation work for making vkms able to support new
features.
Tested-by: Melissa Wen <melissa.srw@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Reviewed-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200830142000.146706-2-rodrigosiqueiramelo@gmail.com

drivers/gpu/drm/vkms/vkms_composer.c

@@ -131,35 +131,31 @@ static void compose_cursor(struct vkms_composer *cursor_composer,
 	      primary_composer, cursor_composer);
 }
 
-static uint32_t _vkms_get_crc(struct vkms_composer *primary_composer,
+static int compose_planes(void **vaddr_out,
+			  struct vkms_composer *primary_composer,
 			  struct vkms_composer *cursor_composer)
 {
 	struct drm_framebuffer *fb = &primary_composer->fb;
 	struct drm_gem_object *gem_obj = drm_gem_fb_get_obj(fb, 0);
 	struct vkms_gem_object *vkms_obj = drm_gem_to_vkms_gem(gem_obj);
-	void *vaddr_out = kzalloc(vkms_obj->gem.size, GFP_KERNEL);
-	u32 crc = 0;
 
-	if (!vaddr_out) {
-		DRM_ERROR("Failed to allocate memory for output frame.");
-		return 0;
+	if (!*vaddr_out) {
+		*vaddr_out = kzalloc(vkms_obj->gem.size, GFP_KERNEL);
+		if (!*vaddr_out) {
+			DRM_ERROR("Cannot allocate memory for output frame.");
+			return -ENOMEM;
 		}
-
-	if (WARN_ON(!vkms_obj->vaddr)) {
-		kfree(vaddr_out);
-		return crc;
 	}
 
-	memcpy(vaddr_out, vkms_obj->vaddr, vkms_obj->gem.size);
-
-	if (cursor_composer)
-		compose_cursor(cursor_composer, primary_composer, vaddr_out);
+	if (WARN_ON(!vkms_obj->vaddr))
+		return -EINVAL;
 
-	crc = compute_crc(vaddr_out, primary_composer);
+	memcpy(*vaddr_out, vkms_obj->vaddr, vkms_obj->gem.size);
 
-	kfree(vaddr_out);
+	if (cursor_composer)
+		compose_cursor(cursor_composer, primary_composer, *vaddr_out);
 
-	return crc;
+	return 0;
 }
 
 /**
@@ -180,9 +176,11 @@ void vkms_composer_worker(struct work_struct *work)
 	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
 	struct vkms_composer *primary_composer = NULL;
 	struct vkms_composer *cursor_composer = NULL;
+	void *vaddr_out = NULL;
 	u32 crc32 = 0;
 	u64 frame_start, frame_end;
 	bool crc_pending;
+	int ret;
 
 	spin_lock_irq(&out->composer_lock);
 	frame_start = crtc_state->frame_start;
@@ -206,14 +204,25 @@ void vkms_composer_worker(struct work_struct *work)
 	if (crtc_state->num_active_planes == 2)
 		cursor_composer = crtc_state->active_planes[1]->composer;
 
-	if (primary_composer)
-		crc32 = _vkms_get_crc(primary_composer, cursor_composer);
+	if (!primary_composer)
+		return;
+
+	ret = compose_planes(&vaddr_out, primary_composer, cursor_composer);
+	if (ret) {
+		if (ret == -EINVAL)
+			kfree(vaddr_out);
+		return;
+	}
+
+	crc32 = compute_crc(vaddr_out, primary_composer);
 
 	/*
 	 * The worker can fall behind the vblank hrtimer, make sure we catch up.
 	 */
 	while (frame_start <= frame_end)
 		drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);
+
+	kfree(vaddr_out);
 }
 
 static const char * const pipe_crc_sources[] = {"auto"};