drm/gem/mod.rs

// SPDX-License-Identifier: GPL-2.0 OR MIT

//! DRM GEM API
//!
//! C header: [`include/linux/drm/drm_gem.h`](srctree/include/linux/drm/drm_gem.h)

use crate::{
    alloc::flags::*,
    bindings, drm,
    drm::driver::{AllocImpl, AllocOps},
    error::{to_result, Result},
    prelude::*,
    types::{ARef, Opaque},
};
use core::{mem, ops::Deref, ptr, ptr::NonNull};

/// GEM object functions, which must be implemented by drivers.
pub trait BaseDriverObject<T: BaseObject>: Sync + Send + Sized {
    /// Create a new driver data object for a GEM object of a given size.
    fn new(dev: &drm::Device<T::Driver>, size: usize) -> impl PinInit<Self, Error>;

    /// Open a new handle to an existing object, associated with a File.
    fn open(
        _obj: &<<T as IntoGEMObject>::Driver as drm::Driver>::Object,
        _file: &drm::File<<<T as IntoGEMObject>::Driver as drm::Driver>::File>,
    ) -> Result {
        Ok(())
    }

    /// Close a handle to an existing object, associated with a File.
    fn close(
        _obj: &<<T as IntoGEMObject>::Driver as drm::Driver>::Object,
        _file: &drm::File<<<T as IntoGEMObject>::Driver as drm::Driver>::File>,
    ) {
    }
}

/// Trait that represents a GEM object subtype
pub trait IntoGEMObject: Sized + super::private::Sealed {
    /// Owning driver for this type
    type Driver: drm::Driver;

    /// Returns a reference to the raw `drm_gem_object` structure, which must be valid as long as
    /// this owning object is valid.
    #[allow(clippy::wrong_self_convention)]
    fn into_gem_obj(&self) -> &Opaque<bindings::drm_gem_object>;

    /// Converts a pointer to a `struct drm_gem_object` into a pointer to `Self`.
    fn from_gem_obj(obj: *mut bindings::drm_gem_object) -> *mut Self;
}

/// Trait which must be implemented by drivers using base GEM objects.
pub trait DriverObject: BaseDriverObject<Object<Self>> {
    /// Parent `Driver` for this object.
    type Driver: drm::Driver;
}

extern "C" fn open_callback<T: BaseDriverObject<U>, U: BaseObject>(
    raw_obj: *mut bindings::drm_gem_object,
    raw_file: *mut bindings::drm_file,
) -> core::ffi::c_int {
    // SAFETY: `open_callback` is only ever called with a valid pointer to a `struct drm_file`.
    let file = unsafe {
        drm::File::<<<U as IntoGEMObject>::Driver as drm::Driver>::File>::as_ref(raw_file)
    };
    let obj =
        <<<U as IntoGEMObject>::Driver as drm::Driver>::Object as IntoGEMObject>::from_gem_obj(
            raw_obj,
        );

    // SAFETY: `from_gem_obj()` returns a valid pointer as long as the type is correct and the
    // `raw_obj` we got is valid.
    match T::open(unsafe { &*obj }, file) {
        Err(e) => e.to_errno(),
        Ok(()) => 0,
    }
}

extern "C" fn close_callback<T: BaseDriverObject<U>, U: BaseObject>(
    raw_obj: *mut bindings::drm_gem_object,
    raw_file: *mut bindings::drm_file,
) {
    // SAFETY: `open_callback` is only ever called with a valid pointer to a `struct drm_file`.
    let file = unsafe {
        drm::File::<<<U as IntoGEMObject>::Driver as drm::Driver>::File>::as_ref(raw_file)
    };
    let obj =
        <<<U as IntoGEMObject>::Driver as drm::Driver>::Object as IntoGEMObject>::from_gem_obj(
            raw_obj,
        );

    // SAFETY: `from_gem_obj()` returns a valid pointer as long as the type is correct and the
    // `raw_obj` we got is valid.
    T::close(unsafe { &*obj }, file);
}

impl<T: DriverObject> IntoGEMObject for Object<T> {
    type Driver = T::Driver;

    fn into_gem_obj(&self) -> &Opaque<bindings::drm_gem_object> {
        &self.obj
    }

    fn from_gem_obj(obj: *mut bindings::drm_gem_object) -> *mut Self {
        // SAFETY: All of our objects are Object<T>.
        unsafe { crate::container_of!(obj, Object<T>, obj).cast_mut() }
    }
}

/// Base operations shared by all GEM object classes
pub trait BaseObject
where
    Self: crate::types::AlwaysRefCounted + IntoGEMObject,
{
    /// Returns the size of the object in bytes.
    fn size(&self) -> usize {
        // SAFETY: `self.into_gem_obj()` is guaranteed to be a pointer to a valid `struct
        // drm_gem_object`.
        unsafe { (*self.into_gem_obj().get()).size }
    }

    /// Creates a new handle for the object associated with a given `File`
    /// (or returns an existing one).
    fn create_handle(
        &self,
        file: &drm::File<<<Self as IntoGEMObject>::Driver as drm::Driver>::File>,
    ) -> Result<u32> {
        let mut handle: u32 = 0;
        // SAFETY: The arguments are all valid per the type invariants.
        to_result(unsafe {
            bindings::drm_gem_handle_create(
                file.as_raw().cast(),
                self.into_gem_obj().get(),
                &mut handle,
            )
        })?;
        Ok(handle)
    }

    /// Looks up an object by its handle for a given `File`.
    fn lookup_handle(
        file: &drm::File<<<Self as IntoGEMObject>::Driver as drm::Driver>::File>,
        handle: u32,
    ) -> Result<ARef<Self>> {
        // SAFETY: The arguments are all valid per the type invariants.
        let ptr = unsafe { bindings::drm_gem_object_lookup(file.as_raw().cast(), handle) };
        let ptr = <Self as IntoGEMObject>::from_gem_obj(ptr);
        let ptr = NonNull::new(ptr).ok_or(ENOENT)?;

        // SAFETY: We take ownership of the reference of `drm_gem_object_lookup()`.
        Ok(unsafe { ARef::from_raw(ptr) })
    }

    /// Creates an mmap offset to map the object from userspace.
    fn create_mmap_offset(&self) -> Result<u64> {
        // SAFETY: The arguments are valid per the type invariant.
        to_result(unsafe { bindings::drm_gem_create_mmap_offset(self.into_gem_obj().get()) })?;

        // SAFETY: The arguments are valid per the type invariant.
        Ok(unsafe {
            bindings::drm_vma_node_offset_addr(ptr::addr_of_mut!(
                (*self.into_gem_obj().get()).vma_node
            ))
        })
    }
}

impl<T> BaseObject for T where Self: crate::types::AlwaysRefCounted + IntoGEMObject {}

/// A base GEM object.
///
/// Invariants
///
/// - `self.obj` is a valid instance of a `struct drm_gem_object`.
/// - `self.dev` is always a valid pointer to a `struct drm_device`.
#[repr(C)]
#[pin_data]
pub struct Object<T: DriverObject + Send + Sync> {
    obj: Opaque<bindings::drm_gem_object>,
    dev: *const drm::Device<T::Driver>,
    #[pin]
    data: T,
}

impl<T: DriverObject> Object<T> {
    /// The size of this object's structure.
    pub const SIZE: usize = mem::size_of::<Self>();

    const OBJECT_FUNCS: bindings::drm_gem_object_funcs = bindings::drm_gem_object_funcs {
        free: Some(Self::free_callback),
        open: Some(open_callback::<T, Object<T>>),
        close: Some(close_callback::<T, Object<T>>),
        print_info: None,
        export: None,
        pin: None,
        unpin: None,
        get_sg_table: None,
        vmap: None,
        vunmap: None,
        mmap: None,
        status: None,
        vm_ops: core::ptr::null_mut(),
        evict: None,
        rss: None,
    };

    /// Create a new GEM object.
    pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
        let obj: Pin<KBox<Self>> = KBox::pin_init(
            try_pin_init!(Self {
                obj: Opaque::new(bindings::drm_gem_object::default()),
                data <- T::new(dev, size),
                // INVARIANT: The drm subsystem guarantees that the `struct drm_device` will live
                // as long as the GEM object lives.
                dev,
            }),
            GFP_KERNEL,
        )?;

        // SAFETY: `obj.as_raw()` is guaranteed to be valid by the initialization above.
        unsafe { (*obj.as_raw()).funcs = &Self::OBJECT_FUNCS };

        // SAFETY: The arguments are all valid per the type invariants.
        to_result(unsafe { bindings::drm_gem_object_init(dev.as_raw(), obj.obj.get(), size) })?;

        // SAFETY: We never move out of `Self`.
        let ptr = KBox::into_raw(unsafe { Pin::into_inner_unchecked(obj) });

        // SAFETY: `ptr` comes from `KBox::into_raw` and hence can't be NULL.
        let ptr = unsafe { NonNull::new_unchecked(ptr) };

        // SAFETY: We take over the initial reference count from `drm_gem_object_init()`.
        Ok(unsafe { ARef::from_raw(ptr) })
    }

    /// Returns the `Device` that owns this GEM object.
    pub fn dev(&self) -> &drm::Device<T::Driver> {
        // SAFETY: The DRM subsystem guarantees that the `struct drm_device` will live as long as
        // the GEM object lives, hence the pointer must be valid.
        unsafe { &*self.dev }
    }

    fn as_raw(&self) -> *mut bindings::drm_gem_object {
        self.obj.get()
    }

    extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) {
        // SAFETY: All of our objects are of type `Object<T>`.
        let this = unsafe { crate::container_of!(obj, Self, obj) }.cast_mut();

        // SAFETY: The C code only ever calls this callback with a valid pointer to a `struct
        // drm_gem_object`.
        unsafe { bindings::drm_gem_object_release(obj) };

        // SAFETY: All of our objects are allocated via `KBox`, and we're in the
        // free callback which guarantees this object has zero remaining references,
        // so we can drop it.
        let _ = unsafe { KBox::from_raw(this) };
    }
}

// SAFETY: Instances of `Object<T>` are always reference-counted.
unsafe impl<T: DriverObject> crate::types::AlwaysRefCounted for Object<T> {
    fn inc_ref(&self) {
        // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
        unsafe { bindings::drm_gem_object_get(self.as_raw()) };
    }

    unsafe fn dec_ref(obj: NonNull<Self>) {
        // SAFETY: `obj` is a valid pointer to an `Object<T>`.
        let obj = unsafe { obj.as_ref() };

        // SAFETY: The safety requirements guarantee that the refcount is non-zero.
        unsafe { bindings::drm_gem_object_put(obj.as_raw()) }
    }
}

impl<T: DriverObject> super::private::Sealed for Object<T> {}

impl<T: DriverObject> Deref for Object<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.data
    }
}

impl<T: DriverObject> AllocImpl for Object<T> {
    const ALLOC_OPS: AllocOps = AllocOps {
        gem_create_object: None,
        prime_handle_to_fd: None,
        prime_fd_to_handle: None,
        gem_prime_import: None,
        gem_prime_import_sg_table: None,
        dumb_create: None,
        dumb_map_offset: None,
    };
}

pub(super) const fn create_fops() -> bindings::file_operations {
    // SAFETY: As by the type invariant, it is safe to initialize `bindings::file_operations`
    // zeroed.
    let mut fops: bindings::file_operations = unsafe { core::mem::zeroed() };

    fops.owner = core::ptr::null_mut();
    fops.open = Some(bindings::drm_open);
    fops.release = Some(bindings::drm_release);
    fops.unlocked_ioctl = Some(bindings::drm_ioctl);
    #[cfg(CONFIG_COMPAT)]
    {
        fops.compat_ioctl = Some(bindings::drm_compat_ioctl);
    }
    fops.poll = Some(bindings::drm_poll);
    fops.read = Some(bindings::drm_read);
    fops.llseek = Some(bindings::noop_llseek);
    fops.mmap = Some(bindings::drm_gem_mmap);
    fops.fop_flags = bindings::FOP_UNSIGNED_OFFSET;

    fops
}