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

[Leif Lindholm <leif.lindholm@linaro.org>]

On Wed, May 24, 2017 at 07:03:10AM -0700, Ard Biesheuvel wrote:
> (+ Leif)
> 
> On 24 May 2017 at 01:34, Scott Telford <stelford@cadence.com> wrote:
> > Hi Ard,
> >
> > Firstly, this patch was meant for my edk2-staging branch, not
> > mainline edk2 - sorry, forgot to edit the subject line!
> 
> Ah ok. In that case, do whatever you like :-)

Well, let's try to get keep the staging branch in a state that doesn't
require too heavy reworking before final upstreaming.

> > 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.
> 
> As I said, the workaround belongs in PciExpressLib. You can just clone
> that and put the workaround in there.
> 
> Interestingly, though, this PCIe IP works fine with the generic ECAM
> driver in Linux, so I wonder what the difference is.
> 
> Leif, were you aware of this issue?

I was not aware of this issue.
So a clone of PciExpressLib, whilst suboptimal, sounds like the way to
go for now.

Regards,

Leif

> >> -----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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