On Sat, Feb 28, 2026 at 07:40:26PM +0100, Danilo Krummrich wrote:
> On Wed Feb 4, 2026 at 9:40 PM CET, Daniel Almeida wrote:
> > This implementation dispatches any work enqueued on ARef<drm::Device<T>> to
> > its driver-provided handler. It does so by building upon the newly-added
> > ARef<T> support in workqueue.rs in order to call into the driver
> > implementations for work_container_of and raw_get_work.
> >
> > This is notably important for work items that need access to the drm
> > device, as it was not possible to enqueue work on a ARef<drm::Device<T>>
> > previously without failing the orphan rule.
> >
> > The current implementation needs T::Data to live inline with drm::Device in
> > order for work_container_of to function. This restriction is already
> > captured by the trait bounds. Drivers that need to share their ownership of
> > T::Data may trivially get around this:
> >
> > // Lives inline in drm::Device
> > struct DataWrapper {
> > work: ...,
> > // Heap-allocated, shared ownership.
> > data: Arc<DriverData>,
> > }
>
> IIUC, this is how it's supposed to be used:
>
> #[pin_data]
> struct MyData {
> #[pin]
> work: Work<drm::Device<MyDriver>>,
> value: u32,
> }
>
> impl_has_work! {
> impl HasWork<drm::Device<MyDriver>> for MyData { self.work }
> }
>
> impl WorkItem for MyData {
> type Pointer = ARef<drm::Device<MyDriver>>;
>
> fn run(dev: ARef<drm::Device<MyDriver>>) {
> dev_info!(dev, "value = {}\n", dev.value);
> }
> }
>
> The reason the WorkItem is implemented for MyData, rather than
> drm::Device<MyDriver> (which would be a bit more straight forward) is the
> orphan
> rule, I assume.
This characterizes it as a workaround for the orphan rule. I don't think
that's fair. Implementing WorkItem for MyDriver directly is the
idiomatic way to do it, in my opinion.
> Now, the whole purpose of this is that a driver can implement WorkItem for
> MyData without needing an additional struct (and allocation), such as:
>
> #[pin_data]
> struct MyWork {
> #[pin]
> work: Work<Self>,
> dev: drm::Device<MyDriver>,
> }
>
> How is this supposed to be done when you want multiple different
> implementations
> of WorkItem that have a drm::Device<MyDriver> as payload?
>
> Fall back to various struct MyWork? Add in an "artificial" type state for
> MyData
> with some phantom data, so you can implement HasWork for MyData<Work0>,
> MyData<Work1>, etc.?
You cannot configure the code that is executed on a per-call basis
because the code called by a work item is a function pointer stored
inside the `struct work_struct`. And it can't be changed after
initialization of the field.
So either you must store that info in a separate field. This is what
Binder does, see drivers/android/binder/process.rs for an example.
impl workqueue::WorkItem for Process {
type Pointer = Arc<Process>;
fn run(me: Arc<Self>) {
let defer;
{
let mut inner = me.inner.lock();
defer = inner.defer_work;
inner.defer_work = 0;
}
if defer & PROC_DEFER_FLUSH != 0 {
me.deferred_flush();
}
if defer & PROC_DEFER_RELEASE != 0 {
me.deferred_release();
}
}
}
Or you must have multiple different fields of type Work, each with a
different function pointer stored inside it.
Note that this is a general workqueue API thing. It's not specific to
ARef<_> or drm::Device<_> based work items, but applies to all users of
the workqueue API.
Alice
