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

["Derrick, Jonathan" <jonathan.derrick@intel.com>]

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@intel.com>
> > ---
> >   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.

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 ||
> >