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Message-ID: <f0dd61c4-f1d8-4c36-a517-91ed5f9e2db3@arm.com>
Date: Mon, 12 Jan 2026 14:09:35 +0000
From: Steven Price <steven.price@....com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>,
Boris Brezillon <boris.brezillon@...labora.com>,
Liviu Dudau <liviu.dudau@....com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Chia-I Wu <olvaffe@...il.com>, Karunika Choo <karunika.choo@....com>
Cc: kernel@...labora.com, linux-kernel@...r.kernel.org,
dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v7 2/4] drm/panthor: Rework panthor_irq::suspended into
panthor_irq::state
On 12/01/2026 13:39, Nicolas Frattaroli wrote:
> On Friday, 9 January 2026 17:05:05 Central European Standard Time Steven Price wrote:
>> On 08/01/2026 14:19, Nicolas Frattaroli wrote:
>>> To deal with the threaded interrupt handler and a suspend action
>>> overlapping, the boolean panthor_irq::suspended is not sufficient.
>>>
>>> Rework it into taking several different values depending on the current
>>> state, and check it and set it within the IRQ helper functions.
>>>
>>> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
>>> ---
>>> drivers/gpu/drm/panthor/panthor_device.h | 40 +++++++++++++++++++++++++-------
>>> 1 file changed, 32 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
>>> index cf76a8abca76..a8c21a7eea05 100644
>>> --- a/drivers/gpu/drm/panthor/panthor_device.h
>>> +++ b/drivers/gpu/drm/panthor/panthor_device.h
>>> @@ -61,6 +61,17 @@ enum panthor_device_pm_state {
>>> PANTHOR_DEVICE_PM_STATE_SUSPENDING,
>>> };
>>>
>>> +enum panthor_irq_state {
>>> + /** @PANTHOR_IRQ_STATE_ACTIVE: IRQ is active and ready to process events. */
>>> + PANTHOR_IRQ_STATE_ACTIVE = 0,
>>> + /** @PANTHOR_IRQ_STATE_PROCESSING: IRQ is currently processing events. */
>>> + PANTHOR_IRQ_STATE_PROCESSING,
>>> + /** @PANTHOR_IRQ_STATE_SUSPENDED: IRQ is suspended. */
>>> + PANTHOR_IRQ_STATE_SUSPENDED,
>>> + /** @PANTHOR_IRQ_STATE_SUSPENDING: IRQ is being suspended. */
>>> + PANTHOR_IRQ_STATE_SUSPENDING,
>>> +};
>>> +
>>> /**
>>> * struct panthor_irq - IRQ data
>>> *
>>> @@ -76,8 +87,8 @@ struct panthor_irq {
>>> /** @mask: Values to write to xxx_INT_MASK if active. */
>>> u32 mask;
>>>
>>> - /** @suspended: Set to true when the IRQ is suspended. */
>>> - atomic_t suspended;
>>> + /** @state: one of &enum panthor_irq_state reflecting the current state. */
>>> + atomic_t state;
>>>
>>> /** @mask_lock: protects modifications to _INT_MASK and @mask */
>>> spinlock_t mask_lock;
>>> @@ -415,7 +426,7 @@ static irqreturn_t panthor_ ## __name ## _irq_raw_handler(int irq, void *data)
>>> \
>>> guard(spinlock_irqsave)(&pirq->mask_lock); \
>>> \
>>> - if (atomic_read(&pirq->suspended)) \
>>> + if (atomic_read(&pirq->state) == PANTHOR_IRQ_STATE_SUSPENDED) \
>>
>> Do we want to also catch the STATE_SUSPENDING case here? AFAICT in
>> SUSPENDING we should be confident that _INT_MASK==0 so this shouldn't a
>> problem (_INT_STAT should read as 0 below). But we don't want interrupts
>> during STATE_SUSPENDING so we might as well handle it.
>
> Depends on what we want to happen here, I think. If the suspend handler
> writing 0 to _INT_MASK does not also happen to clear _INT_STAT, then as
_STAT is defined by the hardware to be the bitwise AND of _RAWSTAT and
_MASK. So we shouldn't see _INT_STAT being anything other than 0.
> far as I can see, we may enter _irq_raw_handler, block for the lock as
> suspend drops it, and then enter the function with STATE_SUSPENDING in
> a context where we'd probably want to process the remaining interrupts
> (i.e. suspend is at synchronise_irq() or about to be there, and we're
> handling the last IRQ that got raised before mask was written to 0).
>
> Let me know if my understanding here is correct, because I think in such
> a case, it's reasonable to process that last IRQ instead of discarding it,
> unless that's something frowned upon that I'm not aware of.
My understanding is that once we have set the status to _SUSPENDING we
don't expect any further interrupts to be fired, but there may be
outstanding interrupts we're still handling. I believe this has to be
the case because AFAIK synchronize_irq() only waits for existing IRQs to
be handled - if another IRQ is triggered during the synchronize_irq()
call then it won't (necessarily) be waited for.
I don't believe the code you have is actually wrong (because the
hardware will mask out any interrupts so _STAT will be zero), but I
personally thought it would be clearer to explicitly handle the
_SUSPENDING state.
Thanks,
Steve
>>
>> Thanks,
>> Steve
>>
>>> return IRQ_NONE; \
>>> if (!gpu_read(ptdev, __reg_prefix ## _INT_STAT)) \
>>> return IRQ_NONE; \
>>> @@ -428,11 +439,14 @@ static irqreturn_t panthor_ ## __name ## _irq_threaded_handler(int irq, void *da
>>> { \
>>> struct panthor_irq *pirq = data; \
>>> struct panthor_device *ptdev = pirq->ptdev; \
>>> + enum panthor_irq_state state; \
>>> irqreturn_t ret = IRQ_NONE; \
>>> u32 mask; \
>>> \
>>> scoped_guard(spinlock_irqsave, &pirq->mask_lock) { \
>>> mask = pirq->mask; \
>>> + atomic_cmpxchg(&pirq->state, PANTHOR_IRQ_STATE_ACTIVE, \
>>> + PANTHOR_IRQ_STATE_PROCESSING); \
>>> } \
>>> \
>>> while (true) { \
>>> @@ -446,11 +460,14 @@ static irqreturn_t panthor_ ## __name ## _irq_threaded_handler(int irq, void *da
>>> } \
>>> \
>>> scoped_guard(spinlock_irqsave, &pirq->mask_lock) { \
>>> - if (!atomic_read(&pirq->suspended)) { \
>>> + state = atomic_read(&pirq->state); \
>>> + if (state != PANTHOR_IRQ_STATE_SUSPENDED && \
>>> + state != PANTHOR_IRQ_STATE_SUSPENDING) { \
>>> /* Only restore the bits that were used and are still enabled */ \
>>> gpu_write(ptdev, __reg_prefix ## _INT_MASK, \
>>> gpu_read(ptdev, __reg_prefix ## _INT_MASK) | \
>>> (mask & pirq->mask)); \
>>> + atomic_set(&pirq->state, PANTHOR_IRQ_STATE_ACTIVE); \
>>> } \
>>> } \
>>> \
>>> @@ -461,16 +478,17 @@ static inline void panthor_ ## __name ## _irq_suspend(struct panthor_irq *pirq)
>>> { \
>>> scoped_guard(spinlock_irqsave, &pirq->mask_lock) { \
>>> gpu_write(pirq->ptdev, __reg_prefix ## _INT_MASK, 0); \
>>> + atomic_set(&pirq->state, PANTHOR_IRQ_STATE_SUSPENDING); \
>>> } \
>>> synchronize_irq(pirq->irq); \
>>> - atomic_set(&pirq->suspended, true); \
>>> + atomic_set(&pirq->state, PANTHOR_IRQ_STATE_SUSPENDED); \
>>> } \
>>> \
>>> static inline void panthor_ ## __name ## _irq_resume(struct panthor_irq *pirq) \
>>> { \
>>> guard(spinlock_irqsave)(&pirq->mask_lock); \
>>> \
>>> - atomic_set(&pirq->suspended, false); \
>>> + atomic_set(&pirq->state, PANTHOR_IRQ_STATE_ACTIVE); \
>>> gpu_write(pirq->ptdev, __reg_prefix ## _INT_CLEAR, pirq->mask); \
>>> gpu_write(pirq->ptdev, __reg_prefix ## _INT_MASK, pirq->mask); \
>>> } \
>>> @@ -494,19 +512,25 @@ static int panthor_request_ ## __name ## _irq(struct panthor_device *ptdev, \
>>> \
>>> static inline void panthor_ ## __name ## _irq_enable_events(struct panthor_irq *pirq, u32 mask) \
>>> { \
>>> + enum panthor_irq_state state; \
>>> + \
>>> guard(spinlock_irqsave)(&pirq->mask_lock); \
>>> \
>>> pirq->mask |= mask; \
>>> - if (!atomic_read(&pirq->suspended)) \
>>> + state = atomic_read(&pirq->state); \
>>> + if (state != PANTHOR_IRQ_STATE_SUSPENDED && state != PANTHOR_IRQ_STATE_SUSPENDING) \
>>> gpu_write(pirq->ptdev, __reg_prefix ## _INT_MASK, pirq->mask); \
>>> } \
>>> \
>>> static inline void panthor_ ## __name ## _irq_disable_events(struct panthor_irq *pirq, u32 mask)\
>>> { \
>>> + enum panthor_irq_state state; \
>>> + \
>>> guard(spinlock_irqsave)(&pirq->mask_lock); \
>>> \
>>> pirq->mask &= ~mask; \
>>> - if (!atomic_read(&pirq->suspended)) \
>>> + state = atomic_read(&pirq->state); \
>>> + if (state != PANTHOR_IRQ_STATE_SUSPENDED && state != PANTHOR_IRQ_STATE_SUSPENDING) \
>>> gpu_write(pirq->ptdev, __reg_prefix ## _INT_MASK, pirq->mask); \
>>> }
>>>
>>>
>>
>>
>
>
>
>
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