Re: [PATCH v2 2/2] PCI/DPC: Allow Native DPC Host Bridges to use DPC

[Kuppuswamy, Sathyanarayanan]

On 4/23/20 8:11 AM, Derrick, Jonathan wrote:
> Hi Sathyanarayanan,
>
> On Wed, 2020-04-22 at 15:50 -0700, Kuppuswamy, Sathyanarayanan wrote:
> > On 4/20/20 2:37 PM, Jon Derrick wrote:
> > > The existing portdrv model prevents DPC services without either OS
> > > control (_OSC) granted to AER services, a Host Bridge requesting Native
> > > AER, or using one of the 'pcie_ports=' parameters of 'native' or
> > > 'dpc-native'.
> > >
> > > The DPC port service driver itself will also fail to probe if the kernel
> > > assumes the port is using Firmware-First AER. It's a reasonable
> > > expectation that a port using Firmware-First AER will also be using
> > > Firmware-First DPC, however if a Host Bridge requests Native DPC, the
> > > DPC driver should allow it and not fail to bind due to AER capability
> > > settings.
> > >
> > > Host Bridges which request Native DPC port services will also likely
> > > request Native AER, however it shouldn't be a requirement. This patch
> > > allows ports on those Host Bridges to have DPC port services.
> > >
> > > This will avoid the unlikely situation where the port is Firmware-First
> > > AER and Native DPC, and a BIOS or switch firmware preconfiguration of
> > > the DPC trigger could result in unhandled DPC events.
> > >
> > > Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
> > > ---
> > >    drivers/pci/pcie/dpc.c          | 3 ++-
> > >    drivers/pci/pcie/portdrv_core.c | 3 ++-
> > >    2 files changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> > > index 7621704..3f3106f 100644
> > > --- a/drivers/pci/pcie/dpc.c
> > > +++ b/drivers/pci/pcie/dpc.c
> > > @@ -284,7 +284,8 @@ static int dpc_probe(struct pcie_device *dev)
> > >    	int status;
> > >    	u16 ctl, cap;
> > >    
> > > -	if (pcie_aer_get_firmware_first(pdev) && !pcie_ports_dpc_native)
> > > +	if (pcie_aer_get_firmware_first(pdev) && !pcie_ports_dpc_native &&
> > > +	    !pci_find_host_bridge(pdev->bus)->native_dpc)
> > Why do it in probe as well ? if host->native_dpc is not set then the
> > device DPC probe it self won't happen right ?
>
> Portdrv only enables the interrupt and allows the probe to occur.

Please check the following snippet of code (from portdrv_core.c).

IIUC, pcie_device_init() will not be called if PCIE_PORT_SERVICE_DPC is
not set in capabilities. Your change in portdrv_core.c already
selectively enables the PCIE_PORT_SERVICE_DPC service based on
native_dpc value.

So IMO, adding native_dpc check in dpc_probe() is redundant.

int pcie_port_device_register(struct pci_dev *dev)
	/* Allocate child services if any */
	status = -ENODEV;
	nr_service = 0;
	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
		int service = 1 << i;
		if (!(capabilities & service))
			continue;
		if (!pcie_device_init(dev, service, irqs[i]))
			nr_service++;
	}

> The probe itself will still fail if there's a mixed-mode _OSC
> negotiated AER & DPC, due to pcie_aer_get_firmware_first returning 1
> for AER and no check for DPC.
>
> I don't know if such a platform will exist, but the kernel is already
> wired for 'dpc-native' so it makes sense to extend it for this..
>
> This transform might be more readable:
> 	if (pcie_aer_get_firmware_first(pdev) &&
> 	    !(pcie_ports_dpc_native || hb->native_dpc))
>
>
>
> > >    		return -ENOTSUPP;
> > >    
> > >    	status = devm_request_threaded_irq(device, dev->irq, dpc_irq,
> > > diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
> > > index 50a9522..f2139a1 100644
> > > --- a/drivers/pci/pcie/portdrv_core.c
> > > +++ b/drivers/pci/pcie/portdrv_core.c
> > > @@ -256,7 +256,8 @@ static int get_port_device_capability(struct pci_dev *dev)
> > >    	 */
> > >    	if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
> > >    	    pci_aer_available() &&
> > > -	    (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
> > > +	    (pcie_ports_dpc_native || host->native_dpc ||
> > > +	     (services & PCIE_PORT_SERVICE_AER)))
> > >    		services |= PCIE_PORT_SERVICE_DPC;
> > >    
> > >    	if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||