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

[Anisa Su <anisa.su887@gmail.com>]

On Wed, Sep 09, 2026 at 10:25:50PM +0530, Shaikh Kamaluddin wrote:
> On Tue, Sep 08, 2026 at 11:22:09AM -0700, Anisa Su wrote:
> > On Sun, Sep 06, 2026 at 09:27:05PM +0530, Shaikh Kamaluddin 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.
> > > 
> > > Fixes: a49aa8141b65 ("cxl/mem: Wire up event interrupts")
> > > 
> > > Signed-off-by: Shaikh Kamaluddin <shaikhkamal2012@gmail.com>
> > Hello,
> > 
> > This looks similar to a patch I sent last week:
> > [PATCH v2 4/4] cxl/events: Return IRQ_NONE when no events were processed
> > https://lore.kernel.org/linux-cxl/8e22c1c2-8098-492a-8162-3dd27507c853@amd.com/T/#ma4cf2b2dddaeebc06cb73f81647817bdbb51963c
> > 
> > It was dropped because I received the feedback that in general, the driver does
> > not need to handle device-side errors/spec-violating behaviors. I believe it
> > would apply here as well. But if I misunderstood the intent of this patch,
> > let me know.
> >
> 
> Hi Anisa,
> 
> Thanks for pointing this out. I came across your v2 patch 4 only after I
> had sent my patch.
> 
> Your patch 4 is based on the preceding robustness changes in the series.
> By that point, cxl_event_thread() has been changed from the original
> do-while loop to a while (mask) loop, and
> cxl_mem_get_event_records() reports both an error return and the set of
> drained logs. The handler also uses the drained and stuck masks to
> control further retries.
> 
> My patch leaves the existing event-record retrieval and do-while loop
> unchanged. It only tracks whether a supported event-status bit was
> observed and uses that information to select IRQ_HANDLED or IRQ_NONE.
> It therefore does not change the handling of mailbox errors, undrained
> logs, or retry behavior.
> 
> The handled tracking in both cases addresses the same zero-status
> shared-vector case. My motivation was its effect on generic IRQ
> spurious-interrupt detection. Jonathan agreed that this is a cleanup
> rather than an interrupt-loss fix, so the Fixes tag should be dropped.
> 
> Since your patch was posted first, would you like to repost the IRQ
> return change as a standalone cleanup? If so, I am happy to step back.
> If you no longer plan to pursue it, I can continue with a v2
> incorporating the review feedback.
> 
> Please let me know which you prefer.
> 
Hello Shaikh,

Thank you for your clarification. Please feel free to continue with v2.
Can you add me to the CC list for v2? I am working on some prepatory
patches for DCD an there would be a minor conflict with this patch,
so I will need to rebase on your changes.

Also Ben Cheatham gave the feedback to mention that "MSI will eventually
be disabled" as a consequence of this patch in the commit message on my patch,
which I think may be valuable here as well:
https://lore.kernel.org/linux-cxl/20260901002912.958-1-anisa.su@samsung.com/T/#m866a4fdb159553039d8d47b6ee7f2312caa9ed73

Thanks,
Anisa

> Thanks,
> Shaikh
> 
> 
> 
> 
> > Thanks,
> > Anisa
> > > ---
> > >  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)
> > >  			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
> > > -- 
> > > 2.43.0
> > >