On Wed, Aug 19, 2026 at 04:37:27PM +0100, Steven Price wrote:
> On 12/08/2026 15:07, Nicolas Frattaroli wrote:
> > panthor_gpu_flush_caches() and panthor_gpu_soft_reset() acquire their
> > reqs_lock spinlock with the IRQ-disabling variants of the spinlocking
> > functions. This isn't necessary, as the lock is never taken from an
> > atomic context, as Panthor uses threaded interrupt handlers. The result
> > of this overly strict locking is that IRQs may be disabled more
> > frequently and for longer than they should be, resulting in increased
> > system latency.
> >
> > Switch the locking to use non-IRQ-disabling scoped_guard statements for
> > locking. The wait_event_timeout read of pending_reqs outside of the
> > spinlock is fine as wait_event_timeout is a memory barrier according to
> > the Linux Memory Model.
> >
> > Fixes: 5cd894e258c4 ("drm/panthor: Add the GPU logical block")
> > Reviewed-by: Boris Brezillon <[email protected]>
> > Signed-off-by: Nicolas Frattaroli <[email protected]>
>
> Reviewed-by: Steven Price <[email protected]>
>
> Although one minor formatting nit below.
>
> > ---
> > drivers/gpu/drm/panthor/panthor_gpu.c | 72
> > ++++++++++++++++-------------------
> > 1 file changed, 33 insertions(+), 39 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c
> > b/drivers/gpu/drm/panthor/panthor_gpu.c
> > index 7088371c6d64..55e33f145b40 100644
> > --- a/drivers/gpu/drm/panthor/panthor_gpu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_gpu.c
> > @@ -345,41 +345,36 @@ int panthor_gpu_flush_caches(struct panthor_device
> > *ptdev,
> > u32 l2, u32 lsc, u32 other)
> > {
> > struct panthor_gpu *gpu = ptdev->gpu;
> > - unsigned long flags;
> > u64 start = 0;
> > int ret = 0;
> >
> > /* Serialize cache flush operations. */
> > guard(mutex)(&ptdev->gpu->cache_flush_lock);
> >
> > - spin_lock_irqsave(&ptdev->gpu->reqs_lock, flags);
> > -
> > - if (tracepoint_enabled(gpu_cache_flush))
> > - start = ktime_get_ns();
> > -
> > - if (!(ptdev->gpu->pending_reqs & GPU_IRQ_CLEAN_CACHES_COMPLETED)) {
> > - ptdev->gpu->pending_reqs |= GPU_IRQ_CLEAN_CACHES_COMPLETED;
> > - gpu_write(gpu->iomem, GPU_CMD, GPU_FLUSH_CACHES(l2, lsc,
> > other));
> > - } else {
> > - ret = -EIO;
> > - }
> > - spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
> > -
> > - if (ret) {
> > - panthor_gpu_emit_flush_caches_tp(ptdev, start, l2, lsc, other,
> > ret);
> > - return ret;
> > + scoped_guard(spinlock, &ptdev->gpu->reqs_lock) {
> > + if (tracepoint_enabled(gpu_cache_flush))
> > + start = ktime_get_ns();
> > +
> > + if (!(ptdev->gpu->pending_reqs &
> > GPU_IRQ_CLEAN_CACHES_COMPLETED)) {
> > + ptdev->gpu->pending_reqs |=
> > GPU_IRQ_CLEAN_CACHES_COMPLETED;
> > + gpu_write(gpu->iomem, GPU_CMD, GPU_FLUSH_CACHES(l2,
> > lsc, other));
> > + } else {
> > + panthor_gpu_emit_flush_caches_tp(ptdev, start, l2, lsc,
> > + other, -EIO);
> > + return -EIO;
> > + }
> > }
> >
> > if (!wait_event_timeout(ptdev->gpu->reqs_acked,
> > !(ptdev->gpu->pending_reqs &
> > GPU_IRQ_CLEAN_CACHES_COMPLETED),
> > msecs_to_jiffies(100))) {
> > - spin_lock_irqsave(&ptdev->gpu->reqs_lock, flags);
> > - if ((ptdev->gpu->pending_reqs & GPU_IRQ_CLEAN_CACHES_COMPLETED)
> > != 0 &&
> > - !(gpu_read(gpu->irq.iomem, INT_RAWSTAT) &
> > GPU_IRQ_CLEAN_CACHES_COMPLETED))
> > - ret = -ETIMEDOUT;
> > - else
> > - ptdev->gpu->pending_reqs &=
> > ~GPU_IRQ_CLEAN_CACHES_COMPLETED;
> > - spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
> > + scoped_guard(spinlock, &ptdev->gpu->reqs_lock) {
> > + if ((ptdev->gpu->pending_reqs &
> > GPU_IRQ_CLEAN_CACHES_COMPLETED) != 0 &&
> > + !(gpu_read(gpu->irq.iomem, INT_RAWSTAT) &
> > GPU_IRQ_CLEAN_CACHES_COMPLETED))
>
> NIT: This isn't aligned correctly with the if() above any more.
I've fixed this locally before pushing it to drm-misc-next.
Best regards,
Liviu
>
> To be honest what we really need here is a helper for this sequence as
> there's basically the same code again in panthor_gpu_soft_reset() below.
>
> > + ret = -ETIMEDOUT;
> > + else
> > + ptdev->gpu->pending_reqs &=
> > ~GPU_IRQ_CLEAN_CACHES_COMPLETED;
> > + }
> > }
> >
> > panthor_gpu_emit_flush_caches_tp(ptdev, start, l2, lsc, other, ret);
> > @@ -402,27 +397,26 @@ int panthor_gpu_soft_reset(struct panthor_device
> > *ptdev)
> > {
> > struct panthor_gpu *gpu = ptdev->gpu;
> > bool timedout = false;
> > - unsigned long flags;
> >
> > - spin_lock_irqsave(&ptdev->gpu->reqs_lock, flags);
> > - if (!drm_WARN_ON(&ptdev->base,
> > - ptdev->gpu->pending_reqs & GPU_IRQ_RESET_COMPLETED)) {
> > - ptdev->gpu->pending_reqs |= GPU_IRQ_RESET_COMPLETED;
> > - gpu_write(gpu->irq.iomem, INT_CLEAR, GPU_IRQ_RESET_COMPLETED);
> > - gpu_write(gpu->iomem, GPU_CMD, GPU_SOFT_RESET);
> > + scoped_guard(spinlock, &ptdev->gpu->reqs_lock) {
> > + if (!drm_WARN_ON(&ptdev->base,
> > + ptdev->gpu->pending_reqs &
> > GPU_IRQ_RESET_COMPLETED)) {
> > + ptdev->gpu->pending_reqs |= GPU_IRQ_RESET_COMPLETED;
> > + gpu_write(gpu->irq.iomem, INT_CLEAR,
> > GPU_IRQ_RESET_COMPLETED);
> > + gpu_write(gpu->iomem, GPU_CMD, GPU_SOFT_RESET);
> > + }
> > }
> > - spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
> >
> > if (!wait_event_timeout(ptdev->gpu->reqs_acked,
> > !(ptdev->gpu->pending_reqs &
> > GPU_IRQ_RESET_COMPLETED),
> > msecs_to_jiffies(100))) {
> > - spin_lock_irqsave(&ptdev->gpu->reqs_lock, flags);
> > - if ((ptdev->gpu->pending_reqs & GPU_IRQ_RESET_COMPLETED) != 0 &&
> > - !(gpu_read(gpu->irq.iomem, INT_RAWSTAT) &
> > GPU_IRQ_RESET_COMPLETED))
> > - timedout = true;
> > - else
> > - ptdev->gpu->pending_reqs &= ~GPU_IRQ_RESET_COMPLETED;
> > - spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
> > + scoped_guard(spinlock, &ptdev->gpu->reqs_lock) {
> > + if ((ptdev->gpu->pending_reqs &
> > GPU_IRQ_RESET_COMPLETED) != 0 &&
> > + !(gpu_read(gpu->irq.iomem, INT_RAWSTAT) &
> > GPU_IRQ_RESET_COMPLETED))
>
> NIT: Same issue here.
>
> Thanks,
> Steve
>
> > + timedout = true;
> > + else
> > + ptdev->gpu->pending_reqs &=
> > ~GPU_IRQ_RESET_COMPLETED;
> > + }
> > }
> >
> > if (timedout) {
> >
>
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
