linux-kernel - Re: [PATCH 2/2] pci: call pci_intx when using legacy interrupts in pci_alloc_irq

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Date:	Thu, 18 Aug 2016 12:33:57 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Christoph Hellwig <hch@....de>
Cc:	linux-pci@...r.kernel.org, helgaas@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] pci: call pci_intx when using legacy interrupts in
 pci_alloc_irq_vectors

On Thu, Aug 18, 2016 at 11:20:07AM +0200, Alexander Gordeev wrote:
> On Thu, Aug 11, 2016 at 07:11:05AM -0700, Christoph Hellwig wrote:
> > ahci currently insists on an explicit call to pci_intx before falling back
> > from MSI or MSI-X to legacy irqs.  As pci_intx is a no-op if the command
> > register already contains the right value is seems safe and useful to add
> > this call to pci_alloc_irq_vectors so that ahci can just use
> > pci_alloc_irq_vectors.
> 
> Looking at ahci_init_interrupts() (and probably at commit d684a90d
> ("ahci: per-port msix support")) it looks like pci_alloc_irq_vectors()
> is able to preserve the current AHCI logic?
     ^^^^
  is *not* able (sorry)

> > Signed-off-by: Christoph Hellwig <hch@....de>
> > ---
> >  drivers/pci/msi.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> > index 9233e7f..593698e 100644
> > --- a/drivers/pci/msi.c
> > +++ b/drivers/pci/msi.c
> > @@ -1200,8 +1200,11 @@ int pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
> >  	}
> >  
> >  	/* use legacy irq if allowed */
> > -	if ((flags & PCI_IRQ_LEGACY) && min_vecs == 1)
> > +	if ((flags & PCI_IRQ_LEGACY) && min_vecs == 1) {
> > +		pci_intx(dev, 1);
> 
> It would rather called pci_intx_for_msi() here. But because it is
> a generic code I am not sure what implications it has for all
> drivers out there.
> 
> >  		return 1;
> > +	}
> > +
> >  	return vecs;
> >  }
> >  EXPORT_SYMBOL(pci_alloc_irq_vectors);
> > -- 
> > 2.1.4
> >