Re: [PATCH 15/17] KVM: PPC: Support irq routing and irqfd for in-kernel MPIC

Alexander Graf
2013-04-25T09:58:51Z

On 19.04.2013, at 20:02, Scott Wood wrote:

> On 04/19/2013 09:06:26 AM, Alexander Graf wrote:
>> diff --git a/Documentation/virtual/kvm/devices/mpic.txt b/Documentation/virtual/kvm/devices/mpic.txt
>> index ce98e32..dadc1e0 100644
>> --- a/Documentation/virtual/kvm/devices/mpic.txt
>> +++ b/Documentation/virtual/kvm/devices/mpic.txt
>> @@ -35,3 +35,14 @@ Groups:
>> "attr" is the IRQ number. IRQ numbers for standard sources are the
>> byte offset of the relevant IVPR from EIVPR0, divided by 32.
>> +
>> +IRQ Routing:
>> +
>> + The MPIC emulation supports IRQ routing. Only a single MPIC device can
>> + be instantiated. Once that device has been created, it's available as
>> + irqchip id 0.
>> +
>
>> + This irqchip 0 has 256 interrupt pins. These pins reflect the SRC pins
>> + on the MPIC controller.
>
> This irqchip 0 has 256 interrupt pins, which expose the interrupts in the main array of interrupt sources (a.k.a. "SRC" interrupts). The numbering is the same as the MPIC device tree binding -- based on the register offset from the beginning of the sources array, without regard to any subdivisions in chip documentation such as "internal" or "external" interrupts. Default routes are established for these pins, with the GSI being equal to the pin number.
>
>> + Access to on-SRC registers is not implemented through IRQ routing mechanisms.
>
> s/on-SRC registers/non-SRC interrupts/
>
>> diff --git a/arch/powerpc/kvm/mpic.c b/arch/powerpc/kvm/mpic.c
>> index 10bc08a..d137df8 100644
>> --- a/arch/powerpc/kvm/mpic.c
>> +++ b/arch/powerpc/kvm/mpic.c
>> @@ -1029,6 +1029,7 @@ static int openpic_cpu_write_internal(void *opaque, gpa_t addr,
>> struct irq_source *src;
>> struct irq_dest *dst;
>> int s_IRQ, n_IRQ;
>> + int notify_eoi = -1;
>> pr_debug("%s: cpu %d addr %#llx <= 0x%08x\n", __func__, idx,
>> addr, val);
>> @@ -1087,6 +1088,8 @@ static int openpic_cpu_write_internal(void *opaque, gpa_t addr,
>> }
>> IRQ_resetbit(&dst->servicing, s_IRQ);
>> + /* Notify listeners that the IRQ is over */
>> + notify_eoi = s_IRQ;
>> /* Set up next servicing IRQ */
>> s_IRQ = IRQ_get_next(opp, &dst->servicing);
>> /* Check queued interrupts. */
>> @@ -1104,6 +1107,12 @@ static int openpic_cpu_write_internal(void *opaque, gpa_t addr,
>> break;
>> }
>> + if (notify_eoi != -1) {
>> + spin_unlock_irq(&opp->lock);
>> + kvm_notify_acked_irq(opp->kvm, 0, notify_eoi);
>> + spin_lock_irq(&opp->lock);
>> + }
>
> I'd rather not have the "_irq" here, which could break if we enter this patch via an "_irqsave" (I realize there currently is no such path that reaches EOI emulation).
>
> Will we ever set notify_eoi when addr != EOI? I'm wondering why it was moved out of the switch statement, instead of being put at the end of the case EOI: code.

I doubt it, but that's for the compiler to optimize away. I found it cleaner for some reason to put it down there. I don't think it really matters.

Alex