drm/vkms: add support for multiple overlay planes

Create 8 overlay planes instead of 1 when the "enable_overlay" module
parameter is set.

The following igt-gpu-tools tests were executed without finding
regressions. Notice than the numbers are identical:

                    |     master branch     |      this  patch      |
                    | SUCCESS | SKIP | FAIL | SUCCESS | SKIP | FAIL |
 kms_atomic         |      10 |   02 |   00 |      10 |   02 |   00 |
 kms_plane_cursor   |      09 |   45 |   00 |      09 |   45 |   00 |
 kms_plane_multiple |      01 |   23 |   00 |      01 |   23 |   00 |
 kms_writeback      |      04 |   00 |   00 |      04 |   00 |   00 |
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220107182809.141003-2-jose.exposito89@gmail.com

drivers/gpu/drm/vkms/vkms_drv.h

@@ -20,6 +20,8 @@
 #define XRES_MAX  8192
 #define YRES_MAX  8192
 
+#define NUM_OVERLAY_PLANES 8
+
 struct vkms_writeback_job {
 	struct dma_buf_map map[DRM_FORMAT_MAX_PLANES];
 	struct dma_buf_map data[DRM_FORMAT_MAX_PLANES];

drivers/gpu/drm/vkms/vkms_output.c

@@ -57,16 +57,19 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
 	struct vkms_plane *primary, *cursor = NULL;
 	int ret;
 	int writeback;
+	unsigned int n;
 
 	primary = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_PRIMARY, index);
 	if (IS_ERR(primary))
 		return PTR_ERR(primary);
 
 	if (vkmsdev->config->overlay) {
+		for (n = 0; n < NUM_OVERLAY_PLANES; n++) {
 			ret = vkms_add_overlay_plane(vkmsdev, index, crtc);
 			if (ret)
 				return ret;
 		}
+	}
 
 	if (vkmsdev->config->cursor) {
 		cursor = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_CURSOR, index);