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    SubjectRe: [PATCH RFC 01/18] rust: drm: ioctl: Add DRM ioctl abstraction
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    On 3/7/23 11:25, Asahi Lina wrote:
    > DRM drivers need to be able to declare which driver-specific ioctls they
    > support. This abstraction adds the required types and a helper macro to
    > generate the ioctl definition inside the DRM driver.
    >
    > Note that this macro is not usable until further bits of the
    > abstraction are in place (but it will not fail to compile on its own, if
    > not called).
    >
    > Signed-off-by: Asahi Lina <lina@asahilina.net>
    > ---
    > drivers/gpu/drm/Kconfig | 7 ++
    > rust/bindings/bindings_helper.h | 2 +
    > rust/kernel/drm/ioctl.rs | 147 ++++++++++++++++++++++++++++++++++++++++
    > rust/kernel/drm/mod.rs | 5 ++
    > rust/kernel/lib.rs | 2 +
    > 5 files changed, 163 insertions(+)
    >
    > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
    > index dc0f94f02a82..dab8f0f9aa96 100644
    > --- a/drivers/gpu/drm/Kconfig
    > +++ b/drivers/gpu/drm/Kconfig
    > @@ -27,6 +27,13 @@ menuconfig DRM
    > details. You should also select and configure AGP
    > (/dev/agpgart) support if it is available for your platform.
    >

    [...]

    > +
    > +/// Declare the DRM ioctls for a driver.
    > +///
    > +/// Each entry in the list should have the form:
    > +///
    > +/// `(ioctl_number, argument_type, flags, user_callback),`
    > +///
    > +/// `argument_type` is the type name within the `bindings` crate.
    > +/// `user_callback` should have the following prototype:
    > +///
    > +/// ```
    > +/// fn foo(device: &kernel::drm::device::Device<Self>,
    > +/// data: &mut bindings::argument_type,
    > +/// file: &kernel::drm::file::File<Self::File>,
    > +/// )
    > +/// ```
    > +/// where `Self` is the drm::drv::Driver implementation these ioctls are being declared within.
    > +///
    > +/// # Examples
    > +///
    > +/// ```
    > +/// kernel::declare_drm_ioctls! {
    > +/// (FOO_GET_PARAM, drm_foo_get_param, ioctl::RENDER_ALLOW, my_get_param_handler),
    > +/// }
    > +/// ```
    > +///
    > +#[macro_export]
    > +macro_rules! declare_drm_ioctls {
    > + ( $(($cmd:ident, $struct:ident, $flags:expr, $func:expr)),* $(,)? ) => {
    > + const IOCTLS: &'static [$crate::drm::ioctl::DrmIoctlDescriptor] = {
    > + const _:() = {
    > + let i: u32 = $crate::bindings::DRM_COMMAND_BASE;
    > + // Assert that all the IOCTLs are in the right order and there are no gaps,
    > + // and that the sizeof of the specified type is correct.

    I believe that not necessarily the IOCTLs need to be in the right order and
    with no gaps. For example, armada_drm.h has a gap in between 0x00 and
    0x02 and exynos_drm.h also have gaps. Moreover, some drivers, like vgem and
    virtgpu, start their IOCTLs with 0x01.

    Best Regards,
    - Maíra Canal

    > + $(
    > + let cmd: u32 = $crate::macros::concat_idents!($crate::bindings::DRM_IOCTL_, $cmd);
    > + ::core::assert!(i == $crate::ioctl::_IOC_NR(cmd));
    > + ::core::assert!(core::mem::size_of::<$crate::bindings::$struct>() == $crate::ioctl::_IOC_SIZE(cmd));
    > + let i: u32 = i + 1;
    > + )*
    > + };
    > +
    > + let ioctls = &[$(
    > + $crate::bindings::drm_ioctl_desc {
    > + cmd: $crate::macros::concat_idents!($crate::bindings::DRM_IOCTL_, $cmd) as u32,
    > + func: {
    > + #[allow(non_snake_case)]
    > + unsafe extern "C" fn $cmd(
    > + raw_dev: *mut $crate::bindings::drm_device,
    > + raw_data: *mut ::core::ffi::c_void,
    > + raw_file_priv: *mut $crate::bindings::drm_file,
    > + ) -> core::ffi::c_int {
    > + // SAFETY: We never drop this, and the DRM core ensures the device lives
    > + // while callbacks are being called.
    > + //
    > + // FIXME: Currently there is nothing enforcing that the types of the
    > + // dev/file match the current driver these ioctls are being declared
    > + // for, and it's not clear how to enforce this within the type system.
    > + let dev = ::core::mem::ManuallyDrop::new(unsafe {
    > + $crate::drm::device::Device::from_raw(raw_dev)
    > + });
    > + // SAFETY: This is just the ioctl argument, which hopefully has the right type
    > + // (we've done our best checking the size).
    > + let data = unsafe { &mut *(raw_data as *mut $crate::bindings::$struct) };
    > + // SAFETY: This is just the DRM file structure
    > + let file = unsafe { $crate::drm::file::File::from_raw(raw_file_priv) };
    > +
    > + match $func(&*dev, data, &file) {
    > + Err(e) => e.to_kernel_errno(),
    > + Ok(i) => i.try_into().unwrap_or(ERANGE.to_kernel_errno()),
    > + }
    > + }
    > + Some($cmd)
    > + },
    > + flags: $flags,
    > + name: $crate::c_str!(::core::stringify!($cmd)).as_char_ptr(),
    > + }
    > + ),*];
    > + ioctls
    > + };
    > + };
    > +}
    > diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
    > new file mode 100644
    > index 000000000000..9ec6d7cbcaf3
    > --- /dev/null
    > +++ b/rust/kernel/drm/mod.rs
    > @@ -0,0 +1,5 @@
    > +// SPDX-License-Identifier: GPL-2.0 OR MIT
    > +
    > +//! DRM subsystem abstractions.
    > +
    > +pub mod ioctl;
    > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
    > index 7903490816bf..cb23d24c6718 100644
    > --- a/rust/kernel/lib.rs
    > +++ b/rust/kernel/lib.rs
    > @@ -37,6 +37,8 @@ mod build_assert;
    > pub mod delay;
    > pub mod device;
    > pub mod driver;
    > +#[cfg(CONFIG_RUST_DRM)]
    > +pub mod drm;
    > pub mod error;
    > pub mod io_buffer;
    > pub mod io_mem;
    >

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