Re: [PATCH v5 00/16] drm/panthor: Reduce dma_fence signalling latency

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

On Thu, 25 Jun 2026 11:36:15 +0200
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> Right now, panthor is one of the rare drivers to signal fences
> from work items (not even from the threaded IRQ handler). We
> tried moving the job_completion check to hardirq handlers like
> other drivers do, but the duration of this handler gets
> slightly over the few usec (20+ usecs) we usually expect from
> hardird handlers, and we're not sure we want to hold off the
> processing of other interrupts for that long. So this series
> just gets rid of the threaded-handler -> work_item indirection
> and checks for job completion (and thus, fence signalling)
> directly in the threaded handler.
> 
> Sorry for the high submission rate (v4 was sent this morning),
> but I'd like get the remaining blockers out of the way, and
> shashiko keeps finding new legitimate issues :-).
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
> Changes in v5:
> - Add a fix for a theoretical IOMEM access in suspended state (patch 1)
> - Make sure we don't delay a pending immediate tick in
>   sched_resume_tick() (patch 2)
> - Make sure we initialize panthor_irq::state properly in the irq_request
>   helper
> - Link to v4: https://lore.kernel.org/r/20260625-panthor-signal-from-irq-v4-0-3d2908912afa@collabora.com
> 
> Changes in v4:
> - Add a bunch of fixes for bugs reported by shashiko
> - Link to v3: https://lore.kernel.org/r/20260623-panthor-signal-from-irq-v3-0-2ece396f8ee0@collabora.com
> 
> Changes in v3:
> - Save/restore the irq state in the raw handler.
> - Rename panthor_irq::mask_lock into panthor_irq::lock
> - Use the __always_inline specifier on
>   panthor_irq_default_threaded_handler()
> - Use devm_request_threaded_irq() even when the threaded handler is
>   NULL
> - Drop the patch that dynamically enables request-related interrupts
>   (FW-side race) after the polling period has expired
> - Don't process FW events from the hardirq handler (too heavy for an
>   hardirq handler according to our testing)
> - Link to v2: https://lore.kernel.org/r/20260512-panthor-signal-from-irq-v2-0-95c614a739cb@collabora.com
> 
> Changes in v2:
> - Fix commit message in patch 4
> - Move devm_kasprintf() before panthor_irq_resume() in patch 3
> - Fix erroneous lockdep_assert_held() in patch 6
> - Make sure events_lock is held when calling
>   csg_slot_sync_update_locked() in patch 6
> - Restore a csg_slot_sync_update_locked() call in patch 7
> - Fix a potential deadlock in patch 9
> - Drop the IRQ coalescing patch (formerly patch 10)
> - Change panthor_irq_request() so we don't have to define a dummy
>   threaded handler, and we can let RT kernels move the hard handler
>   to a thread
> - Add patches to transition GPU event processing to the hard IRQ handler
> - Link to v1: https://lore.kernel.org/r/20260429-panthor-signal-from-irq-v1-0-4b92ae4142d2@collabora.com
> 
> ---
> Boris Brezillon (16):
>       drm/panthor: Fix theoretical IOMEM access in suspended state
>       drm/panthor: Don't overrule pending immediate ticks in sched_resume_tick()
>       drm/panthor: Fix panthor_pwr_unplug()
>       drm/panthor: Drop a needless check in panthor_fw_unplug()
>       drm/panthor: Fix a leak when a group is evicted before the tiler OOM is serviced
>       drm/panthor: Interrupt group start/resumption if group_bind_locked() fails
>       drm/panthor: Keep interrupts masked until they are needed

If you're reviewing this version, please ignore anything coming before
patch 8, since those have been re-posted as a separate misc-fixes
series[1].

Thanks,

Boris

>       drm/panthor: Make panthor_irq::state a non-atomic field
>       drm/panthor: Move the register accessors before the IRQ helpers
>       drm/panthor: Replace the panthor_irq macro machinery by inline helpers
>       drm/panthor: Don't update might_have_idle_groups in process_idle_event_locked()
>       drm/panthor: Get rid of panthor_group::fatal_lock
>       drm/panthor: Protect events processing with a separate spinlock
>       drm/panthor: Don't defer job completion checks
>       drm/panthor: Don't defer FW event processing
>       drm/panthor: Automate CSG IRQ processing at group unbind time

[1]https://lore.kernel.org/dri-devel/20260625-panthor-misc-fixes-v1-0-b67ed973fea6@collabora.com/T/#t