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

[Shaikh Kamaluddin]

On Mon, Sep 07, 2026 at 07:48:24PM +0100, Jonathan Cameron wrote:
> 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?
>
Hi Jonathan,
No interrupts are lost. I agree that it only affects spurious
interrupt detection.

When note_interrupt() receives IRQ_WAKE_THREAD, it sets
SPURIOUS_DEFERRED and checks on the next interrupt whether
desc->threads_handled changed. Currently, cxl_event_thread() returns
IRQ_HANDLED even for zero event status, incrementing that counter and
making an unrelated interrupt appear handled.

Returning IRQ_NONE for zero status leaves the counter unchanged. Another
handler sharing the vector can still claim the interrupt; otherwise,
note_interrupt() can account it as unhandled. Normal CXL event handling
is unchanged, so I agree this should be presented as a cleanup without a Fixes tag.

> > 
> > 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!
>

Sorry It was my mistake

> > 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.
> 
> >  			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
>