[PATCH] PCI: Add pcie_irq=other to enable non MSI/INTx interrupt for port service driver

[Liu Shengzhou-B36685]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, July 10, 2012 12:39 AM
> To: Liu Shengzhou-B36685
> Cc: bhelgaas at google.com; linux-pci at vger.kernel.org; linuxppc-
> dev at lists.ozlabs.org
> Subject: Re: [PATCH] PCI: Add pcie_irq=other to enable non MSI/INTx interrupt
> for port service driver
> 
> On 07/09/2012 05:49 AM, Shengzhou Liu wrote:
> > On some platforms, in RC mode, root port has neither MSI/MSI-X nor
> > INTx interrupt generated, which are available only in EP mode on those
> platform.
> > In this case, we try to use other interrupt if supported (i.e. there
> > is the shared error interrupt on platform P1010, P3041, P4080, etc) to
> > have AER, Hot-plug, etc, services to work.
> >
> > Signed-off-by: Shengzhou Liu <Shengzhou.Liu at freescale.com>
> > ---
> >  Documentation/kernel-parameters.txt |    4 ++++
> >  drivers/pci/pcie/portdrv_core.c     |   19 +++++++++++++++++++
> >  2 files changed, 23 insertions(+), 0 deletions(-)
> >
> > diff --git a/Documentation/kernel-parameters.txt
> > b/Documentation/kernel-parameters.txt
> > index a92c5eb..af97c81 100644
> > --- a/Documentation/kernel-parameters.txt
> > +++ b/Documentation/kernel-parameters.txt
> > @@ -2218,6 +2218,10 @@ bytes respectively. Such letter suffixes can also be
> entirely omitted.
> >  		nomsi	Do not use MSI for native PCIe PME signaling (this makes
> >  			all PCIe root ports use INTx for all services).
> >
> > +	pcie_irq=	[PCIE] Native PCIe root port interrupt options:
> > +		other	Try to use other interrupt when root port has
> > +			neither MSI/MSI-X nor INTx support.
> 
> Why does the user need to specify this?  Shouldn't this be a matter of
> communication between kernel internals?
> 

The "other interrupt" appears a non-standard interrupt way compared to MSI/MSI-X and INTx in point of PCIe spec.
The intent of specifying this is to have an intervention and confirmation manually to avoid causing unexpected issue on some unknown platforms.
I'm glad to remove the specified kernel parameter if it would be accepted upstream.

> > @@ -216,6 +227,14 @@ static int init_service_irqs(struct pci_dev *dev, int
> *irqs, int mask)
> >  	if (!pci_enable_msi(dev) || dev->pin)
> >  		irq = dev->irq;
> >
> > +	/*
> > +	 * On some platforms, root port has neither MSI/MSI-X nor INTx
> > +	 * interrupt support in RC mode, so try to use other interrupt(i.e.
> > +	 * shared interrupt if supported).
> > +	 */
> > +	else if (port_other_interrupt_enabled && dev->irq)
> > +		irq = dev->irq;
> 
> Is there any reason to not use dev->irq if it is non-zero?
> 
> -Scott

I guess a thinking of the original author did so is based on the point of PCIe spec, whether INTx is supported or not is decided by the "PCI Express Interrupt Pin Register(Read only)".

Is there the case on some other unknown platforms that dev->irq is non-zero due to incorrect initialization of irq allocation, but actually it doesn't support MSI/MSIX/INTx or any other interrupt?  
If we don't need to consider this case, we can use dev->irq directly instead of dev->pin to support "other interrupt".

Thanks,
Shengzhou