Re: [Xen-devel] [PATCH v2 09/45] ARM: GIC: Allow tweaking the active and pending state of an IRQ

[Andre Przywara <andre.przywara@xxxxxxxxxx>]

Hi,

On 19/03/18 09:30, Julien Grall wrote:
> 
> 
> On 03/16/2018 04:05 PM, Andre Przywara wrote:
>> Hi,
> 
> Hi Andre,
> 
>> On 15/03/18 20:30, Andre Przywara wrote:
>>> +    }
>>> +}
>>> +
>>> +static void gicv2_set_pending_state(struct irq_desc *irqd, bool
>>> pending)
>>> +{
>>> +    ASSERT(spin_is_locked(&irqd->lock));
>>> +
>>> +    if ( pending )
>>> +    {
>>> +        /* The INPROGRESS bit will be set when the interrupt fires. */
>>> +        gicv2_poke_irq(irqd, GICD_ISPENDR);
>>> +    }
>>> +    else
>>> +    {
>>> +        gicv2_poke_irq(irqd, GICD_ICPENDR);
>>> +        if ( !gicv2_peek_irq(irqd, GICD_ISACTIVER) &&
>>> +             test_bit(_IRQ_GUEST, &irqd->status) )
>>> +            clear_bit(_IRQ_INPROGRESS, &irqd->status);
>>
>> We should not need to touch the _IRQ_INPROGRESS bit here. That bit
>> really shadows the *active* bit, so changing the pending state should
>> not matter here:
>> - If the h/w IRQ is active, the bit is set already and should remain so,
>> as Xen and the guest are still dealing with it. Clearing the h/w pending
>> state does not change that.
>> - If the h/w IRQ is not active, the _IRQ_INPROGRESS bit is not set, so
>> clearing it would be a NOP.
>> So we can remove  the _IRQ_INPROGRESS handling here completely.
>>
>> I will amend the code accordingly, including the respective GICv3 parts.
> 
> Thank you for summarizing our discussion. Is it still making sense to
> document how those helpers should be called?

Which helpers? The set_{pending,active}_state() functions? I already put
some kind of warning before the (wrapper) prototypes:
/*
 * Set the active state of an IRQ. This should be used with care, as
 * this directly forces the active bit, without considering the GIC
 * state machine.
 * For private IRQs this only works for those of the current CPU.
 */

Cheers,
Andre.

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