Re: [PATCH] Copy bus scanning workaround from ARM Juno PCIe driver.

[Scott Telford <stelford@cadence.com>]

Hi Ard,

Firstly, this patch was meant for my edk2-staging branch, not mainline edk2 - sorry, forgot to edit the subject line!

The issue is that, without this workaround, PCI(e) bridges and devices will be detected multiple times during bus scanning, e.g. a bridge at bus 1 device 0 will also be seen at bus 1 device 1, bus 1 device 2 etc and hence all the devices on the other side of the bridge will be duplicated too. I copied this workaround from the old Juno PCIe driver as I was seeing the same problem when I was testing the Cadence PCIe host bridge library I have been working on. I agree there should probably be a more elegant solution, but I don't know the generic PCI driver code well enough to suggest one at the moment.


Regards,
Scott.

> -----Original Message-----
> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
> Sent: 23 May 2017 17:42
> To: Scott Telford <stelford@cadence.com>
> Cc: edk2-devel@lists.01.org <edk2-devel@ml01.01.org>; Tian, Feng
> <feng.tian@intel.com>; Zeng, Star <star.zeng@intel.com>
> Subject: Re: [edk2] [PATCH] Copy bus scanning workaround from ARM Juno
> PCIe driver.
> 
> On 23 May 2017 at 09:15, Scott Telford <stelford@cadence.com> wrote:
> > Copy workaround previously in
> >
> ArmPlatformPkg/ArmJunoPkg/Drivers/PciHostBridgeDxe/PciRootBridge.c:Pci
> RbPciRead()
> > to RootBridgeIoPciAccess(), to avoid spurious multiple detections when
> > scanning buses.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.0
> > Signed-off-by: Scott Telford <stelford@cadence.com>
> > ---
> >  MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c | 13
> +++++++++++++
> 
> This does not belong in the generic driver.
> 
> Could you please explain in more detail what the issue is? In any
> case, we will need to put this workaround in a Juno specific
> implementation of PciExpressLib
> 
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c
> b/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c
> > index a0e7e5b..3cca3c1 100644
> > --- a/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c
> > +++ b/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c
> > @@ -945,6 +945,19 @@ RootBridgeIoPciAccess (
> >      PciAddress.ExtendedRegister = PciAddress.Register;
> >    }
> >
> > +  // The UEFI PCI enumerator scans for devices at all possible addresses,
> > +  // and ignores some PCI rules - this results in some hardware being
> > +  // detected multiple times. We work around this by faking absent
> > +  // devices
> > +  if ((PciAddress.Bus == 0) && ((PciAddress.Device != 0) ||
> (PciAddress.Function != 0))) {
> > +    *((UINT32 *)Buffer) = 0xffffffff;
> > +    return EFI_SUCCESS;
> > +  }
> > +  if ((PciAddress.Bus == 1) && ((PciAddress.Device != 0) ||
> (PciAddress.Function != 0))) {
> > +    *((UINT32 *)Buffer) = 0xffffffff;
> > +    return EFI_SUCCESS;
> > +  }
> > +
> >    Address = PCI_SEGMENT_LIB_ADDRESS (
> >                RootBridge->RootBridgeIo.SegmentNumber,
> >                PciAddress.Bus,
> > --
> > 2.2.2
> >
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