Re: [PATCH 07/12] drm/tyr: Add generic slot manager

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 27 Feb 2026 16:28:51 -0800
Deborah Brouwer <deborah.brouwer@collabora.com> wrote:

> > >   
> > >> 
> > >> access vs access_mut() does not matter here: since the owner is &mut self
> > >> anyways we know we have exclusive access to the LockedSeat throughout the whole
> > >> function.  
> > > 
> > > I agree, but LockedBy is picky, and last I tried I couldn't make it
> > > work without the annoying update+return-copy-of-seat dance you see
> > > here. Maybe I missed something obvious and it does indeed work with
> > > your suggested changes, dunno.  
> > 
> > Rewriting things so they pass the borrow checker is common in Rust. Sometimes
> > it can be done rather easily; other times the design is just broken and needs
> > to be reworked. Luckily this one fell in the first category.
> > 
> > This benefits from the fact that no one can race us between reading this tuple
> > 
> > (slot_idx, seqno, is_active) 
> > 
> > ..and using it. That’s because we’re taking &mut self as a proxy in LockedBy, so
> > we’re sure we have exclusive access in this scope.

Yep, I know that, but I seem to remember it wasn't working when I was doing

        match locked_seat.access(self) {
            Seat::Active(seat_info) | Seat::Idle(seat_info) => {
                // With lazy eviction, if seqno matches, the hardware state is still
                // valid for both Active and Idle slots, so just update our records
                self.record_active_slot(seat_info.slot as usize, locked_seat, slot_data)
            }
            _ => self.allocate_slot(locked_seat, slot_data),
        }

in ::activate(), which is why I made check_seat() return a Seat and
did the match against this returned seat. Oh well, I must have
misunderstood the problem reported by the compiler.

> > 
> > If you don’t have any complaints about the code I sent (i.e.: convoluted, wrong
> > logic, etc), I suggest switching to it.  
> 
> I’ve tested the short check_seat() function and can confirm that it correctly
> compares Seat and Slot seqno as well as emits the kernel warning when we have a
> mismatch on an active Seat. So I’ll the simplified check_seat() function in v2
> unless there are any more issues to address.

If things still compile/work as expected, no objection on my end.