egl-gbm: fix for kms display-only rendering

The tegra-drm + nvidia-drm setup on r36 is tenuous with respect
to egl-gbm (and particularly calls to eglGetPlatformDisplayEXT with
EGL_PLATFORM_GBM_KHR). It was only working somewhat by chance due
to the order that devices are probed and then made available to
readdir().

This change adds a patch to egl-gbm to provide a fallback in the
case where eglGetPlatformDisplayEXT(EGL_PLATFORM_GBM_KHR) might have
otherwise failed for no good reason, thus eliminating the need for
workarounds to enforce ordering of the modules loading.

Signed-off-by: Kurt Kiefer <kekiefer@gmail.com>

recipes-graphics/mesa/egl-gbm/0001-gbm-display-handle-kms-display-only-devices-in-FindG.patch

@@ -0,0 +1,41 @@
+From f28f8e7e7013ed151ab69ae6b0f4b52ef617dc89 Mon Sep 17 00:00:00 2001
+From: Kurt Kiefer <kekiefer@gmail.com>
+Date: Thu, 29 Aug 2024 15:15:33 -0700
+Subject: [PATCH] gbm-display: handle kms display-only devices in FindGbmDevice
+
+A display device can be different than its renderer, such as the
+case of a kms display-only device. Yet, eglGbmGetPlatformDisplay
+needs to initialize its internal GbmDisplay structure and if they
+aren't strongly associated (as determined by eglQueryDevices) then
+display initialization will fail.
+
+Handle this by providing a fallback to use the first renderer
+returned by eglQueryDevices in the case where the display device
+in question can't render on its own or isn't being returned by
+the egl implementation for any other reason.
+
+Upstream-status: pending
+
+Signed-off-by: Kurt Kiefer <kekiefer@gmail.com>
+---
+ src/gbm-display.c | 7 +++++++
+ 1 file changed, 7 insertions(+)
+
+diff --git a/src/gbm-display.c b/src/gbm-display.c
+index 93bceb4..3144017 100644
+--- a/src/gbm-display.c
++++ b/src/gbm-display.c
+@@ -119,6 +119,13 @@ FindGbmDevice(GbmPlatformData* data, struct gbm_device* gbm)
+         }
+     }
+ 
++    // If we didn't find a device, don't panic. This can happen if the gbm
++    // display device isn't a renderer: a kms display-only device, or a split
++    // host1x + drm/kms display such as t234 machines in r36. Use the first
++    // found renderer for these.
++    if (numDevs > 0)
++        dev = devs[0];
++
+ done:
+     free(devs);
+ 

recipes-graphics/mesa/egl-gbm_1.1.0.bb

@@ -6,14 +6,13 @@ DEPENDS = "eglexternalplatform libdrm virtual/libgbm"
 
 SRC_REPO = "github.com/NVIDIA/egl-gbm.git;protocol=https"
 SRCBRANCH = "main"
-SRC_URI = "git://${SRC_REPO};branch=${SRCBRANCH}"
+SRC_URI = "git://${SRC_REPO};branch=${SRCBRANCH} \
+           file://nvidia_gbm.json \
+           file://0001-gbm-display-handle-kms-display-only-devices-in-FindG.patch \
+           "
 # 1.1.0 tag
 SRCREV = "39932b2cc4f44cdadd553cc931f3bebd4e348d10"
 
-SRC_URI += "\
-    file://nvidia_gbm.json \
-"
-
 REQUIRED_DISTRO_FEATURES = "opengl"
 
 S = "${WORKDIR}/git"