Hi Lyude,
> On 30 Sep 2024, at 20:10, Lyude Paul <lyude@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> ---
> 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 }
> + }
Shouldn’t this be introduced by the patch that introduced `num_plane()` directly?
> +
> + /// 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
>
>
Barring the comment above, it overall LGTM.
— Daniel
