linux-kernel - Re: [PATCH v1 1/1] mfd: intel-lpss: Switch over to MSI interrupts

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Date: Tue, 26 Mar 2024 16:01:07 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] mfd: intel-lpss: Switch over to MSI interrupts

On Tue, Mar 26, 2024 at 06:21:47PM +0200, Andy Shevchenko wrote:
> On Mon, Mar 25, 2024 at 04:19:15PM -0500, Bjorn Helgaas wrote:
> > On Tue, Mar 12, 2024 at 06:59:05PM +0200, Andy Shevchenko wrote:
> 
> ...
> 
> > > -	ret = pci_alloc_irq_vectors(pdev, 1, 1, PCI_IRQ_LEGACY);
> > > +	ret = pci_alloc_irq_vectors(pdev, 1, 1, PCI_IRQ_ALL_TYPES);
> > >  	if (ret < 0)
> > >  		return ret;
> > 
> > I guess at least some of these devices do support INTx, since we
> > always used INTx previously, right?
> > 
> > There are a bunch of bug reports complaining about a lack of _PRT
> > entries for them, e.g., these from
> > https://bugzilla.kernel.org/show_bug.cgi?id=212261#c24:
> 
> But this is not related to my patch, and the mentioned bug report seems about
> all AMD and Intel platforms.
> 
> Can you, please, elaborate what the relation to my patch?

Right, sorry I didn't make that clear; I didn't mean that it was
related to your patch.  I was just looking at this old bug report
about not being able to figure out INTx routing.

Your patch had to do with interrupts, so I just wondered whether you
had insight into whether these devices actually used INTx.  My guess
is that at least some of them *do* use INTx, because prior to your
patch, the driver *only* tried to use INTx.

If it happend that they never use INTx, but advertise INTA via
Interrupt Pin, I think that would be a device defect that we might
consider a quirk for.

If they *do* use INTx, and the _PRT doesn't tell us how it's routed, I
think that would be a firmware defect, and ... I dunno what we would
do.  I guess just avoid using INTx because we don't know where the
interupt goes.

Bjorn