From: Daniel Golle <daniel@makrotopia.org>
Date: Mon, 25 May 2026 22:00:00 +0100
Subject: zink: allow KMS-only display fd to fall through to default
 Vulkan device selection

When MESA_LOADER_DRIVER_OVERRIDE=zink is used with a GBM device created
on a KMS-only display node (e.g. /dev/dri/card1 bound to verisilicon-dc
on StarFive JH7110), zink_render_rdev() returned -1 because the device
has no render node, causing zink_drm_create_screen() to bail and GBM
initialisation to fail.

Treat the missing render node as "no specific device requested" instead
of an error.  zink_picks_device() then returns false, and choose_pdev()
falls back to default Vulkan physical-device selection, picking
whichever ICD vkEnumeratePhysicalDevices() reports first (PowerVR on
JH7110).  Cross-device dma-buf import via VK_KHR_external_memory_fd
takes care of getting the rendered frame onto the display controller.

--- a/src/gallium/drivers/zink/zink_screen.c
+++ b/src/gallium/drivers/zink/zink_screen.c
@@ -3862,10 +3862,15 @@ zink_render_rdev(int fd, int64_t *dev_ma
    if (drmGetDevice2(fd, 0, &dev))
       return -1;
 
-   if(!(dev->available_nodes & (1 << DRM_NODE_RENDER))) {
-      ret = -1;
+   /*
+    * If the fd points to a KMS-only display device with no render node,
+    * leave dev_major/dev_minor unset.  choose_pdev() will then fall back
+    * to default Vulkan physical-device selection, allowing zink to drive
+    * a render-only GPU (e.g. PowerVR via VK_KHR_external_memory_fd) on
+    * top of a separate display controller (e.g. verisilicon-dc).
+    */
+   if(!(dev->available_nodes & (1 << DRM_NODE_RENDER)))
       goto free_device;
-   }
 
    if(stat(dev->nodes[DRM_NODE_RENDER], &stx)) {
       ret = -1;