[Xen-devel] Why xen-pirq chip use startup_irq() for .irq_enable?

[shuo.a.liu@xxxxxxxxx]

Hi,
Here is a device has xen-pirq-MSI interrupt. I found dom0 might lost
interrupt during driver irq_disable/irq_enable.
There is a pair of irq_disable/enable in driver. Here is the scenario,
 1. irq_disable(dev_irq) -> disable_dynirq -> mask_evtchn(dev_irq channel)
 2. dev interrupt raised by HW and Xen mark its evtchn as *pending* status.
 3. irq_enable(dev_irq) -> startup_pirq -> eoi_pirq ->
    clear_evtchn(channel of dev_irq) -> clear *pending* status
 4. consume_one_event process the dev irq event without pending bit assert
    which result in interrupt lost once.
 5. No HW interrupt raising anymore.

The first question here is why using startup_irq for .irq_enable rather than
enable_dynirq ? startup_irq will do eoi_pirq who clear the mask bit and pending
bit of the channel while enable_dynirq just only unmask the channel.

Second question is that what's the purpose of eoi_pirq in startup_irq?

BTW, i can resolve my problem by below patch. Does it make sence?

---
drivers/xen/events/events_base.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 4bf7a34..341c456 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -582,7 +582,7 @@ static void shutdown_pirq(struct irq_data *data)

static void enable_pirq(struct irq_data *data)
{
-       startup_pirq(data);
+       enable_dynirq(data);
}

static void disable_pirq(struct irq_data *data)
--


Thanks.
Shuo A


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