[PATCH] irqchip/exynos-combiner: switch to raw_spinlock

[Marek Szyprowski]

On 21.05.2026 11:06, Thomas Gleixner wrote:
> On Thu, May 21 2026 at 00:04, Marek Szyprowski wrote:
>> The exynos-combiner driver uses a regular spinlock to protect access to
>> the combiner interrupt status register in combiner_handle_cascade_irq(),
>> which is invoked in hard IRQ context as a chained interrupt handler.
>>
>> When PREEMPT_RT is enabled on ARM, regular spinlock is converted to a
>> sleeping lock (mutex-based), which must not be used in atomic context
>> such as hard interrupt handlers. Switch the irq_controller_lock to
>> raw_spinlock, which remains a true non-sleeping spinlock even under
>> PREEMPT_RT.
> Mechanically this makes sense, but out of curiosity I have to ask:
>
>> -static DEFINE_SPINLOCK(irq_controller_lock);
>> +static DEFINE_RAW_SPINLOCK(irq_controller_lock);
>>  
>>  struct combiner_chip_data {
>>  	unsigned int hwirq_offset;
>> @@ -72,9 +72,9 @@ static void combiner_handle_cascade_irq(struct irq_desc *desc)
>>  
>>  	chained_irq_enter(chip, desc);
>>  
>> -	spin_lock(&irq_controller_lock);
>> +	raw_spin_lock(&irq_controller_lock);
>>  	status = readl_relaxed(chip_data->base + COMBINER_INT_STATUS);
>> -	spin_unlock(&irq_controller_lock);
>> +	raw_spin_unlock(&irq_controller_lock);
> What is this lock actually protecting?
>
> Each combiner has it's own @base address, so there is no concurrency
> problem between two cascade interrupts being handled at the same time.
>
> That means the only possible problem would be that the same cascade
> interrupt is handled on two CPUs concurrently. Is that even possible?
Frankly speaking I did this conversion mechanically, late in the evening to fix
the bug warning I've spotted. Indeed this spinlock looks like a copy&paste or
development leftover. The only side-effect of it I see is a memory barrier,
which might affect how the register access happens, but this should not affect
cascade operation imho. Do You want me to send a patch removing it completely?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland