Re: [PATCH] cxl/events: Return IRQ_NONE when no event is pending

[Jonathan Cameron]

On Wed, 9 Sep 2026 10:08:14 +0800
Li Ming <ming.li@xxxxxxxxxxxx> wrote:

> 在 2026/9/8 02:48, Jonathan Cameron 写道:
> > On Sun,  6 Sep 2026 21:27:05 +0530
> > Shaikh Kamaluddin <shaikhkamal2012@xxxxxxxxx> wrote:
> >  
> >> CXL event interrupts may share an MSI/MSI-X vector with other event
> >> logs or device features. Consequently, cxl_event_thread() is registered
> >> with IRQF_SHARED and must determine whether an interrupt belongs to the
> >> event-log facility.
> >>
> >> The handler masks the Device Event Status register to the event logs
> >> supported by the driver. However, when no supported status bit is set,
> >> it exits the processing loop and still returns IRQ_HANDLED.
> >>
> >> Track whether at least one supported event status bit was observed.
> >> Return IRQ_NONE when there was no event to service, while continuing to
> >> return IRQ_HANDLED after processing one or more event logs.  
> > What is the practical result of this change?
> > I think it will only affect the spurious interrupt detection so
> > to me it looks like a cleanup rather than a fix.  Is there
> > any path by which we actually lose interrupts as a result of this?
> >  
> >> Fixes: a49aa8141b65 ("cxl/mem: Wire up event interrupts")
> >>  
> > No blank lines in tag blocks.  There are a number of tools that rely
> > on there not being any and as such there are also scripts that run
> > on various upstream trees that will send us annoying emails if this
> > blank line is still here!  I'm not sure why this mistake in patch
> > formatting is so common as there are plenty of docs without the
> > blank lines!
> >  
> >> Signed-off-by: Shaikh Kamaluddin <shaikhkamal2012@xxxxxxxxx>  
> > A suggestion for an alternative implementation below.
> >  
> >> ---
> >>   drivers/cxl/pci.c | 5 ++++-
> >>   1 file changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> >> index c7c91e8dc51d..8b560cae91f2 100644
> >> --- a/drivers/cxl/pci.c
> >> +++ b/drivers/cxl/pci.c
> >> @@ -515,6 +515,7 @@ static irqreturn_t cxl_event_thread(int irq, void *id)
> >>   	struct cxl_dev_id *dev_id = id;
> >>   	struct cxl_dev_state *cxlds = dev_id->cxlds;
> >>   	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlds);
> >> +	bool handled = false;
> >>   	u32 status;
> >>   
> >>   	do {
> >> @@ -527,11 +528,13 @@ static irqreturn_t cxl_event_thread(int irq, void *id)
> >>   		status &= CXLDEV_EVENT_STATUS_ALL;
> >>   		if (!status)  
> > 			return IRQ_NONE;
> >
> > And don't need the other changes.  
> 
> Hi Jonathan,
> 
> 
> I think we should not return IRQ_NONE here, because the loop could run 
> multiple times untill no event record, so we always get a status with 
> 0x0 value in the last loop. In that case, we still need to return 
> IRQ_HANDLED.

Ah excellent point.  Ignore me.  Any dance to return here needs
a handled variable to be checked so ends up just being moving the
return.  Maybe that's worth doing but not important.

Jonathan

> 
> 
> Ming
> 
> >  
> >>   			break;
> >> +
> >> +		handled = true;
> >>   		cxl_mem_get_event_records(mds, status);
> >>   		cond_resched();
> >>   	} while (status);
> >>   
> >> -	return IRQ_HANDLED;
> >> +	return handled ? IRQ_HANDLED : IRQ_NONE;
> >>   }
> >>   
> >>   static int cxl_event_req_irq(struct cxl_dev_state *cxlds, u8 setting)
> >>
> >> base-commit: 7098e9cd98a05c0c5de2fae0c2465f9d966fdd07
> >> prerequisite-patch-id: 92e40cd60a697020faac475dcc77ba63b33434ea
> >> prerequisite-patch-id: 10027ad5d9aed85806047f807b3a76273b6c4a77