diff --git a/drmu/drmu_output.c b/drmu/drmu_output.c
index c6a9eaf..7797e29 100644
--- a/drmu/drmu_output.c
+++ b/drmu/drmu_output.c
@@ -472,13 +472,12 @@ try_conn_crtc(drmu_env_t * du, drmu_conn_t * dn, drmu_crtc_t * dc)
 }
 
 int
-drmu_atomic_output_add_writeback_fb(drmu_atomic_t * const da_out, drmu_output_t * const dout,
-                                    drmu_fb_t * const dfb)
+drmu_atomic_output_add_writeback_fb_mode(drmu_atomic_t * const da_out, drmu_output_t * const dout,
+                                         drmu_fb_t * const dfb, const struct drm_mode_modeinfo *mode)
 {
     drmu_env_t * const du = dout->du;
     drmu_atomic_t * da = drmu_atomic_new(drmu_atomic_env(da_out));
     int rv = -ENOMEM;
-    struct drm_mode_modeinfo mode = modeinfo_fake(drmu_fb_width(dfb), drmu_fb_height(dfb));
     drmu_conn_t * const dn = dout->dns[0];
 
     if (da == NULL)
@@ -488,7 +487,7 @@ drmu_atomic_output_add_writeback_fb(drmu_atomic_t * const da_out, drmu_output_t
         drmu_err(du, "Failed to add FB to conn");
         goto fail;
     }
-    if ((rv = drmu_atomic_crtc_add_modeinfo(da, dout->dc, &mode)) != 0) {
+    if ((rv = drmu_atomic_crtc_add_modeinfo(da, dout->dc, mode)) != 0) {
         drmu_err(du, "Failed to add modeinfo to CRTC");
         goto fail;
     }
@@ -508,6 +507,15 @@ drmu_atomic_output_add_writeback_fb(drmu_atomic_t * const da_out, drmu_output_t
     return rv;
 }
 
+int
+drmu_atomic_output_add_writeback_fb(drmu_atomic_t * const da_out, drmu_output_t * const dout,
+                                    drmu_fb_t * const dfb)
+{
+    struct drm_mode_modeinfo mode = modeinfo_fake(drmu_fb_width(dfb), drmu_fb_height(dfb));
+
+    return drmu_atomic_output_add_writeback_fb_mode(da_out, dout, dfb, &mode);
+}
+
 int
 drmu_output_add_writeback(drmu_output_t * const dout)
 {
diff --git a/drmu/drmu_output.h b/drmu/drmu_output.h
index 5ec2d71..96fe2ff 100644
--- a/drmu/drmu_output.h
+++ b/drmu/drmu_output.h
@@ -55,6 +55,9 @@ int drmu_output_modeset_allow(drmu_output_t * const dout, const bool allow);
 // If != NULL then 1st conn with prefix-matching name is used
 int drmu_output_add_output(drmu_output_t * const dout, const char * const conn_name);
 
+// Set writeback fb on output with user specified mode
+int drmu_atomic_output_add_writeback_fb_mode(drmu_atomic_t * const da_req, drmu_output_t * const dout,
+                                    drmu_fb_t * const dfb, const struct drm_mode_modeinfo *mode);
 // Set writeback fb on output
 int drmu_atomic_output_add_writeback_fb(drmu_atomic_t * const da_req, drmu_output_t * const dout,
                                     drmu_fb_t * const dfb);
diff --git a/test/10bittest.c b/test/10bittest.c
index 93b29fd..fbb6a11 100644
--- a/test/10bittest.c
+++ b/test/10bittest.c
@@ -301,6 +301,7 @@ usage()
            "-M  drm module name, default: " DRM_MODULE "\n"
            "-v  verbose\n"
            "-w  write to writeback rather than screen, then writen to wb.rgb\n"
+           "-t  transpose writeback output\n"
            "\n"
            "Hit return to exit\n"
            "\n"
@@ -311,6 +312,25 @@ usage()
     exit(1);
 }
 
+static void create_drm_mode(struct drm_mode_modeinfo * mode, int width, int height)
+{
+    mode->clock = width * height * 60;
+    mode->hdisplay = width;
+    mode->hsync_start = width;
+    mode->hsync_end = width;
+    mode->htotal = width;
+    mode->hskew = 0;
+    mode->vdisplay = height;
+    mode->vsync_start = height;
+    mode->vsync_end = height;
+    mode->vtotal = height;
+    mode->vscan = 0;
+    mode->vrefresh = 60;
+    mode->type = DRM_MODE_TYPE_USERDEF;
+    mode->flags = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC;
+    strcpy(mode->name, "fake");
+}
+
 int main(int argc, char *argv[])
 {
     drmu_env_t * du = NULL;
@@ -338,7 +358,7 @@ int main(int argc, char *argv[])
     bool mode_req = false;
     bool hi_bpc = true;
     bool dofrac = false;
-    bool try_writeback = false;
+    bool try_writeback = false, try_transpose = false;
     int verbose = 0;
     int c;
     uint64_t fillval = p16val(~0U, 0x8000, 0x8000, 0x8000);
@@ -346,7 +366,7 @@ int main(int argc, char *argv[])
     unsigned int p16_stride = 0;
     int rv;
 
-    while ((c = getopt(argc, argv, "8c:e:f:FgpM:P:r:R:svwy")) != -1) {
+    while ((c = getopt(argc, argv, "8c:e:f:FgpM:P:r:R:stvwy")) != -1) {
         switch (c) {
             case 'c':
                 colorspace = optarg;
@@ -431,6 +451,9 @@ int main(int argc, char *argv[])
             case 'w':
                 try_writeback = true;
                 break;
+            case 't':
+                try_transpose = true;
+                break;
             case 'v':
                 ++verbose;
                 break;
@@ -498,17 +521,22 @@ int main(int argc, char *argv[])
     drmu_output_max_bpc_allow(dout, hi_bpc);
 
     if (try_writeback) {
+        struct drm_mode_modeinfo mode = { 0 };
+
         if (!mp.width || !mp.height) {
             mp.width = 1920;
             mp.height = 1080;
         }
+
         printf("Try writeback %dx%d\n", mp.width, mp.height);
 
-        if ((fb_out = drmu_fb_new_dumb(du, mp.width, mp.height, DRM_FORMAT_ARGB8888)) == NULL) {
+        if ((fb_out = drmu_fb_new_dumb(du, try_transpose ? mp.height : mp.width,
+                                       try_transpose ? mp.width : mp.height, DRM_FORMAT_ARGB8888)) == NULL) {
             printf("Failed to create fb-out\n");
             goto fail;
         }
-        if (drmu_atomic_output_add_writeback_fb(da, dout, fb_out) != 0) {
+        create_drm_mode(&mode , mp.width, (mp.height + 15) & ~15);
+        if (drmu_atomic_output_add_writeback_fb_mode(da, dout, fb_out, &mode) != 0) {
             printf("Failed to add writeback fb\n");
             goto fail;
         }