Make DRM support optional.

The DRM API is for interacting with GPUs and displays directly via
system calls, without going through something like Mesa. Very few
`wgpu` users are driving hardware directly, and those that are are
sophisticated users, capable of finding and requesting the feature
themselves.

Supporting DRM in `wgpu_hal` adds dependencies on `drm` and its
supporting crates. The crates seem fine, but they do contribute to
download and build time.

Firefox definitely does not want to have to vendor `drm` and its
subcrates into its source tree, since Firefox should never be
interacting with graphics hardware directly.

In `wgpu_hal`, make support for `RawWindowHandle::Drm` and
`RawDisplayHandle::Drm` require that the `"drm"` feature be explicitly
requested, rather than supporting DRM handles by default.

Add a `"drm"` feature to `wgpu`, `wgpu-core`, and
`wgpu-core-deps-windows-linux-android`, and make the relevant glue
code conditional on that.

Author: jimblandy

CHANGELOG.md

@@ -62,7 +62,9 @@ Bottom level categories:
 
 #### Vulkan
 
-- Add support for RawWindowHandle::Drm on unix. By @rectalogic in [#9182](https://github.com/gfx-rs/wgpu/pull/9182).
+- Add support for RawWindowHandle::Drm on unix, conditional on the `"drm"` feature.
+    - DRM support by @rectalogic in [#9182](https://github.com/gfx-rs/wgpu/pull/9182).
+    - Conditional compilation by @jimblandy in [#9390](https://github.com/gfx-rs/wgpu/pull/9390)
 
 ### Changes
 

wgpu-core/Cargo.toml

@@ -149,6 +149,9 @@ vulkan-portability = ["wgpu-core-deps-apple/vulkan-portability"]
 ## Renderdoc integration, only available on Windows, Linux, and Android
 renderdoc = ["wgpu-core-deps-windows-linux-android/renderdoc"]
 
+## Support creating textures from DRM display/window handles.
+drm = ["wgpu-core-deps-windows-linux-android/drm"]
+
 ## Enable the `noop` backend.
 # TODO(https://github.com/gfx-rs/wgpu/issues/7120): there should be a hal feature
 noop = []

wgpu-core/platform-deps/windows-linux-android/Cargo.toml

@@ -22,6 +22,9 @@ vulkan = ["wgpu-hal/vulkan"]
 dx12 = ["wgpu-hal/dx12"]
 renderdoc = ["wgpu-hal/renderdoc"]
 
+## Support creating textures from DRM display/window handles.
+drm = ["wgpu-hal/drm"]
+
 # Depend on wgpu-hal conditionally, so that the above features only apply to wgpu-hal on this set of platforms.
 [target.'cfg(any(windows, target_os = "linux", target_os = "android", target_os = "freebsd", target_os = "netbsd"))'.dependencies]
 wgpu-hal.workspace = true

wgpu-core/src/instance.rs

@@ -261,14 +261,10 @@ impl Instance {
     ///
     /// # Platform Support
     ///
-    /// This function is only available on non-apple Unix-like platforms (Linux, FreeBSD) and
-    /// currently only works with the Vulkan backend.
-    #[cfg(all(
-        unix,
-        not(target_vendor = "apple"),
-        not(target_family = "wasm"),
-        not(target_os = "netbsd")
-    ))]
+    /// This function requires the `"drm"` feature. It is only available on
+    /// non-apple Unix-like platforms (Linux, FreeBSD) and currently only works
+    /// with the Vulkan backend.
+    #[cfg(feature = "drm")]
     #[cfg_attr(not(vulkan), expect(unused_variables))]
     pub unsafe fn create_surface_from_drm(
         &self,
@@ -968,12 +964,7 @@ impl Global {
     ///
     /// This function is only available on non-apple Unix-like platforms (Linux, FreeBSD) and
     /// currently only works with the Vulkan backend.
-    #[cfg(all(
-        unix,
-        not(target_vendor = "apple"),
-        not(target_family = "wasm"),
-        not(target_os = "netbsd")
-    ))]
+    #[cfg(feature = "drm")]
     pub unsafe fn instance_create_surface_from_drm(
         &self,
         fd: i32,

wgpu-hal/Cargo.toml

@@ -94,7 +94,6 @@ vulkan = [
     "dep:arrayvec",
     "dep:ash",
     "dep:bytemuck",
-    "dep:drm",
     "dep:gpu-descriptor",
     "dep:hashbrown",
     "dep:libc",
@@ -252,6 +251,7 @@ wayland-sys = { version = "0.31.3", features = [
     "egl",
 ], optional = true }
 
+## Support creating textures from DRM display/window handles.
 [target.'cfg(all(unix, not(target_vendor = "apple"), not(target_family = "wasm")))'.dependencies]
 drm = { version = "0.15", optional = true }
 

wgpu-hal/src/vulkan/drm.rs

@@ -1,4 +1,4 @@
-#![cfg(all(unix, not(target_vendor = "apple"), not(target_family = "wasm")))]
+#![cfg(feature = "drm")]
 
 use alloc::{string::ToString, vec::Vec};
 use core::{mem::MaybeUninit, num::NonZeroU32};

wgpu-hal/src/vulkan/instance.rs

@@ -264,11 +264,7 @@ impl super::Instance {
             extensions.push(ext::metal_surface::NAME);
             extensions.push(khr::portability_enumeration::NAME);
         }
-        if cfg!(all(
-            unix,
-            not(target_vendor = "apple"),
-            not(target_family = "wasm")
-        )) {
+        if cfg!(feature = "drm") {
             // VK_EXT_acquire_drm_display -> VK_EXT_direct_mode_display -> VK_KHR_display
             extensions.push(ext::acquire_drm_display::NAME);
             extensions.push(ext::direct_mode_display::NAME);
@@ -892,7 +888,7 @@ impl crate::Instance for super::Instance {
                 let connection = display.connection.expect("Pointer to X-Server is not set.");
                 self.create_surface_from_xcb(connection.as_ptr(), handle.window.get())
             }
-            #[cfg(all(unix, not(target_vendor = "apple"), not(target_family = "wasm")))]
+            #[cfg(feature = "drm")]
             (Rwh::Drm(handle), Rdh::Drm(display)) => {
                 self.create_surface_from_drm_plane(display.fd, handle.plane)
             }

wgpu/Cargo.toml

@@ -85,6 +85,11 @@ vulkan-portability = ["wgpu-core?/vulkan-portability"]
 ## Enables the GLES backend on WebAssembly only.
 webgl = ["web", "wgpu-core/webgl", "dep:wgpu-hal", "dep:smallvec"]
 
+#! ### Backend features
+
+## Support creating textures from DRM display/window handles.
+drm = ["wgpu-core/drm"]
+
 ## Enables the noop backend for testing.
 ##
 ## This backend allows creating resources such as buffers and textures,

wgpu/src/backend/wgpu_core.rs

@@ -792,12 +792,21 @@ impl dispatch::InstanceInterface for ContextWgpuCore {
                     .instance_create_surface(raw_display_handle, raw_window_handle, None)
             },
 
-            #[cfg(all(
-                unix,
-                not(target_vendor = "apple"),
-                not(target_family = "wasm"),
-                not(target_os = "netbsd")
-            ))]
+            #[cfg(target_os = "netbsd")]
+            SurfaceTargetUnsafe::Drm { .. } => Err(
+                wgc::instance::CreateSurfaceError::BackendNotEnabled(wgt::Backend::Vulkan),
+            ),
+
+            #[cfg(not(any(feature = "drm", target_os = "netbsd")))]
+            SurfaceTargetUnsafe::Drm { .. } => {
+                return Err(crate::CreateSurfaceError {
+                    inner: crate::CreateSurfaceErrorKind::RawHandle(
+                        raw_window_handle::HandleError::NotSupported,
+                    ),
+                });
+            }
+
+            #[cfg(any(feature = "drm", target_os = "netbsd"))]
             SurfaceTargetUnsafe::Drm {
                 fd,
                 plane,
@@ -822,11 +831,6 @@ impl dispatch::InstanceInterface for ContextWgpuCore {
                 self.0.instance_create_surface_metal(layer, None)
             },
 
-            #[cfg(target_os = "netbsd")]
-            SurfaceTargetUnsafe::Drm { .. } => Err(
-                wgc::instance::CreateSurfaceError::BackendNotEnabled(wgt::Backend::Vulkan),
-            ),
-
             #[cfg(dx12)]
             SurfaceTargetUnsafe::CompositionVisual(visual) => unsafe {
                 self.0.instance_create_surface_from_visual(visual, None)