Subject: [PATCH 2/2] aer: add support aer interrupt with none MSI/MSI-X/INTx mode

From: [email-masked] (Bjorn Helgaas)
Date: Thu, 2 Jun 2016 08:55:46 -0500

On Thu, Jun 02, 2016 at 05:01:19AM +0000, Po Liu wrote:
> >  -----Original Message-----
> >  From: Bjorn Helgaas [mailto:helgaas at kernel.org]
> >  Sent: Thursday, June 02, 2016 11:48 AM
> >  To: Po Liu
> >  Cc: linux-pci at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
> >  linux-kernel at vger.kernel.org; devicetree at vger.kernel.org; Arnd Bergmann;
> >  Roy Zang; Marc Zyngier; Stuart Yoder; Yang-Leo Li; Minghuan Lian; Bjorn
> >  Helgaas; Shawn Guo; Mingkai Hu; Rob Herring
> >  Subject: Re: [PATCH 2/2] aer: add support aer interrupt with none
> >  MSI/MSI-X/INTx mode
> >  
> >  [+cc Rob]
> >  
> >  Hi Po,
> >  
> >  On Thu, May 26, 2016 at 02:00:06PM +0800, Po Liu wrote:
> >  > On some platforms, root port doesn't support MSI/MSI-X/INTx in RC mode.
> >  > When chip support the aer interrupt with none MSI/MSI-X/INTx mode,
> >  > maybe there is interrupt line for aer pme etc. Search the interrupt
> >  > number in the fdt file.
> >  
> >  My understanding is that AER interrupt signaling can be done via INTx,
> >  MSI, or MSI-X (PCIe spec r3.0, sec 6.2.4.1.2).  Apparently your device
> >  doesn't support MSI or MSI-X.  Are you saying it doesn't support INTx
> >  either?  How is the interrupt you're requesting here different from INTx?
> 
> Layerscape use none of MSI or MSI-X or INTx to indicate the devices
> or root error in RC mode. But use an independent SPI interrupt(arm
> interrupt controller) line.  

The Root Port is a PCI device and should follow the normal PCI rules
for interrupts.  As far as I understand, that means it should use MSI,
MSI-X, or INTx.  If your Root Port doesn't use MSI or MSI-X, it should
use INTx, the PCI_INTERRUPT_PIN register should tell us which (INTA/
INTB/etc.), and PCI_COMMAND_INTX_DISABLE should work to disable it.
That's all from the PCI point of view, of course.

What's on the other end of those interrupts is outside the scope of
PCI.  An INTx interrupt (either a conventional PCI wire or a PCIe
virtual INTx wire) might be connected to an IOAPIC, an ARM SPI, or
something else.  Drivers should not care about how it is connected,
and that's why I don't think this code really fits in portdrv.

Maybe your Root Port is non-compliant in some way and maybe we need a
quirk or something to work around that hardware defect.  But I'm not
convinced yet that we have that sort of problem.  It seems like we
just don't have the correct DT description.

> And at same time, AER capability list
> in PCIe register descriptors. And also, The Root Error
> Command/status register was proper to enable/disable the AER
> interrupt.

I'm not sure what you're saying here.  Here's what I think you said;
please correct me if I'm wrong:

  - Your Root Port has an AER capability.

  - Your Root Port does not support MSI or MSI-X.  (This would
    actually be a spec violation because the PCIe spec r3.0, sec 7.7
    says "All PCI Express device Functions that are capable of
    generating interrupts must implement MSI or MSI-X or both.")
  
  - The three enable bits in the Root Error Command Register enable or
    disable generation of interrupts.  These enable bits control all
    interrupts, whether MSI, MSI-X, or INTx.

  - The Root Error Status Register contains an "Advanced Error
    Interrupt Message Number" field, but that's only applicable if MSI
    or MSI-X is enabled, and if your device doesn't support MSI or
    MSI-X, this field doesn't apply.

> This hardware implementation make sense in some platforms, and this
> was described in the function init_service_irqs() in the
> drivers/pci/pcie/portdrv_core.c in current kernel as:

> 
> 241      * We're not going to use MSI-X, so try MSI and fall back to INTx.     
> 242      * If neither MSI/MSI-X nor INTx available, try other interrupt.  On  
> 243      * some platforms, root port doesn't support MSI/MSI-X/INTx in RC mode
> 244      */                                                                             
> 
> So I think this was the proper place to update the irq number before aer service
> driver was loaded.
> 
> >  
> >  My guess is that your device *does* support INTx, and we should use that.
> >  ACPI has the generic _PRT that describes INTx routing.  There must be
> >  something similar for DT, but I don't know what it is.  It seems like
> >  this should be described using that DT mechanism (whatever it is), and
> >  we shouldn't need special-case code in the portdrv code.
> >  
> >  > Signed-off-by: Po Liu <[email-masked]>
> >  > ---
> >  >  drivers/pci/pcie/portdrv_core.c | 31 ++++++++++++++++++++++++++++---
> >  >  1 file changed, 28 insertions(+), 3 deletions(-)
> >  >
> >  > diff --git a/drivers/pci/pcie/portdrv_core.c
> >  > b/drivers/pci/pcie/portdrv_core.c index 32d4d0a..64833e5 100644
> >  > --- a/drivers/pci/pcie/portdrv_core.c
> >  > +++ b/drivers/pci/pcie/portdrv_core.c
> >  > @@ -15,6 +15,7 @@
> >  >  #include <linux/slab.h>
> >  >  #include <linux/pcieport_if.h>
> >  >  #include <linux/aer.h>
> >  > +#include <linux/of_irq.h>
> >  >
> >  >  #include "../pci.h"
> >  >  #include "portdrv.h"
> >  > @@ -199,6 +200,28 @@ static int pcie_port_enable_msix(struct pci_dev
> >  > *dev, int *vectors, int mask)  static int init_service_irqs(struct
> >  > pci_dev *dev, int *irqs, int mask)  {
> >  >  	int i, irq = -1;
> >  > +	int ret;
> >  > +	struct device_node *np = NULL;
> >  > +
> >  > +	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++)
> >  > +		irqs[i] = 0;
> >  > +
> >  > +	if (dev->bus->dev.of_node)
> >  > +		np = dev->bus->dev.of_node;
> >  > +
> >  > +	/* If root port doesn't support MSI/MSI-X/INTx in RC mode,
> >  > +	 * request irq for aer
> >  > +	 */
> >  > +	if (IS_ENABLED(CONFIG_OF_IRQ) && np &&
> >  > +			(mask & PCIE_PORT_SERVICE_PME)) {
> >  > +		ret = of_irq_get_byname(np, "aer");
> >  > +		if (ret > 0) {
> >  > +			irqs[PCIE_PORT_SERVICE_AER_SHIFT] = ret;
> >  > +			if (dev->irq)
> >  > +				irq = dev->irq;
> >  > +			goto no_msi;
> >  > +		}
> >  > +	}
> >  >
> >  >  	/*
> >  >  	 * If MSI cannot be used for PCIe PME or hotplug, we have to use
> >  @@
> >  > -224,11 +247,13 @@ static int init_service_irqs(struct pci_dev *dev,
> >  int *irqs, int mask)
> >  >  		irq = dev->irq;
> >  >
> >  >   no_msi:
> >  > -	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++)
> >  > -		irqs[i] = irq;
> >  > +	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
> >  > +		if (!irqs[i])
> >  > +			irqs[i] = irq;
> >  > +	}
> >  >  	irqs[PCIE_PORT_SERVICE_VC_SHIFT] = -1;
> >  >
> >  > -	if (irq < 0)
> >  > +	if (irq < 0 && irqs[PCIE_PORT_SERVICE_AER_SHIFT] < 0)
> >  >  		return -ENODEV;
> >  >  	return 0;
> >  >  }
> >  > --
> >  > 2.1.0.27.g96db324
> >  >
> >  >
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