[WIP RFC v2 32/35] rust: drm/kms: Add Device::num_crtcs()

[Lyude Paul]

A binding for checking drm_device.num_crtcs. We'll need this in a moment
for vblank support, since setting it up requires knowing the number of
CRTCs that a driver has initialized.

Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 rust/kernel/drm/kms.rs | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/drm/kms.rs b/rust/kernel/drm/kms.rs
index 3edd90bc0025a..d0745b44ba9b6 100644
--- a/rust/kernel/drm/kms.rs
+++ b/rust/kernel/drm/kms.rs
@@ -253,10 +253,27 @@ pub fn mode_config_lock(&self) -> ModeConfigGuard<'_, T> {
 
     /// Return the number of registered [`Plane`](plane::Plane) objects on this [`Device`].
     #[inline]
-    pub fn num_plane(&self) -> i32 {
-        // SAFETY: The only context which this could change is before registration, which must be
-        // single-threaded anyway - so it's safe to just read this value
-        unsafe { (*self.as_raw()).mode_config.num_total_plane }
+    pub fn num_plane(&self) -> u32 {
+        // SAFETY:
+        // * This can only be modified during the single-threaded context before registration, so
+        //   this is safe
+        // * num_total_plane could be >= 0, but no less - so casting to u32 is fine (and better to
+        //   prevent errors)
+        unsafe { (*self.as_raw()).mode_config.num_total_plane as u32 }
+    }
+
+    /// Return the number of registered CRTCs
+    /// TODO: while `num_crtc` is of i32, that type actually makes literally no sense here and just
+    /// causes problems and unecessary casts. Same for num_plane(). So, fix that at some point (we
+    /// will never get n < 0 anyway)
+    #[inline]
+    pub fn num_crtcs(&self) -> u32 {
+        // SAFETY:
+        // * This can only be modified during the single-threaded context before registration, so
+        //   this is safe
+        // * num_crtc could be >= 0, but no less - so casting to u32 is fine (and better to prevent
+        //   errors)
+        unsafe { (*self.as_raw()).mode_config.num_crtc as u32 }
     }
 }
 
-- 
2.46.1