[RFC v3 25/33] rust: drm/kms: Add drm_framebuffer bindings

[Lyude Paul <lyude@redhat.com>]

This adds some very simple bindings for drm_framebuffer. We don't use them
much yet, but we'll eventually be using them when rvkms eventually gets CRC
and writeback support. Just like Connector objects, these use RcModeObject.

Signed-off-by: Lyude Paul <lyude@redhat.com>

---

V3:
* Replace Framebuffer struct with tuple
* Add safety comments for ModeObject implementation
* Add comment for why we're using Sealed

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 rust/bindings/bindings_helper.h    |  1 +
 rust/kernel/drm/kms.rs             |  1 +
 rust/kernel/drm/kms/framebuffer.rs | 74 ++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+)
 create mode 100644 rust/kernel/drm/kms/framebuffer.rs

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 846eb6eb8fc4c..2e80a62062fc8 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -18,6 +18,7 @@
 #include <drm/drm_file.h>
 #include <drm/drm_fbdev_dma.h>
 #include <drm/drm_fbdev_shmem.h>
+#include <drm/drm_framebuffer.h>
 #include <drm/drm_gem.h>
 #include <drm/drm_gem_framebuffer_helper.h>
 #include <drm/drm_gem_shmem_helper.h>
diff --git a/rust/kernel/drm/kms.rs b/rust/kernel/drm/kms.rs
index 978bb6712ffbe..429ce28229c9e 100644
--- a/rust/kernel/drm/kms.rs
+++ b/rust/kernel/drm/kms.rs
@@ -6,6 +6,7 @@
 pub mod connector;
 pub mod crtc;
 pub mod encoder;
+pub mod framebuffer;
 pub mod plane;
 
 use crate::{
diff --git a/rust/kernel/drm/kms/framebuffer.rs b/rust/kernel/drm/kms/framebuffer.rs
new file mode 100644
index 0000000000000..5a60b580fe0bf
--- /dev/null
+++ b/rust/kernel/drm/kms/framebuffer.rs
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+//! DRM framebuffers.
+//!
+//! C header: [`include/drm/drm_framebuffer.h`](srctree/include/drm/drm_framebuffer.h)
+
+use super::{KmsDriver, ModeObject, RcModeObject};
+use crate::{drm::device::Device, types::*};
+use bindings;
+use core::{marker::*, ptr};
+
+/// The main interface for [`struct drm_framebuffer`].
+///
+/// # Invariants
+///
+/// - `self.0` is initialized for as long as this object is exposed to users.
+/// - This type has an identical data layout to [`struct drm_framebuffer`]
+///
+/// [`struct drm_framebuffer`]: srctree/include/drm/drm_framebuffer.h
+#[repr(transparent)]
+pub struct Framebuffer<T: KmsDriver>(Opaque<bindings::drm_framebuffer>, PhantomData<T>);
+
+// SAFETY:
+// - `self.0` is initialized for as long as this object is exposed to users
+// - `base` is initialized by DRM when `self.0` is initialized, thus `raw_mode_obj()` always returns
+//   a valid pointer.
+unsafe impl<T: KmsDriver> ModeObject for Framebuffer<T> {
+    type Driver = T;
+
+    fn drm_dev(&self) -> &Device<Self::Driver> {
+        // SAFETY: `dev` points to an initialized `struct drm_device` for as long as this type is
+        // initialized
+        unsafe { Device::borrow((*self.0.get()).dev) }
+    }
+
+    fn raw_mode_obj(&self) -> *mut bindings::drm_mode_object {
+        // SAFETY: We don't expose Framebuffer<T> to users before its initialized, so `base` is
+        // always initialized
+        unsafe { ptr::addr_of_mut!((*self.0.get()).base) }
+    }
+}
+
+// SAFETY: Framebuffers are refcounted mode objects.
+unsafe impl<T: KmsDriver> RcModeObject for Framebuffer<T> {}
+
+// SAFETY: References to framebuffers are safe to be accessed from any thread
+unsafe impl<T: KmsDriver> Send for Framebuffer<T> {}
+// SAFETY: References to framebuffers are safe to be accessed from any thread
+unsafe impl<T: KmsDriver> Sync for Framebuffer<T> {}
+
+// For implementing ModeObject
+impl<T: KmsDriver> crate::private::Sealed for Framebuffer<T> {}
+
+impl<T: KmsDriver> PartialEq for Framebuffer<T> {
+    fn eq(&self, other: &Self) -> bool {
+        ptr::eq(self.0.get(), other.0.get())
+    }
+}
+impl<T: KmsDriver> Eq for Framebuffer<T> {}
+
+impl<T: KmsDriver> Framebuffer<T> {
+    /// Convert a raw pointer to a `struct drm_framebuffer` into a [`Framebuffer`]
+    ///
+    /// # Safety
+    ///
+    /// The caller guarantews that `ptr` points to a initialized `struct drm_framebuffer` for at
+    /// least the entire lifetime of `'a`.
+    #[inline]
+    #[allow(dead_code)]
+    pub(super) unsafe fn from_raw<'a>(ptr: *const bindings::drm_framebuffer) -> &'a Self {
+        // SAFETY: Our data layout is identical to drm_framebuffer
+        unsafe { &*ptr.cast() }
+    }
+}
-- 
2.48.1