I checked the UEFI shell implementation. It uses below:
//
// If this is not a multi-function device, we can leave the
loop
// to deal with the next device.
//
if (Func == 0 && ((PciHeader.HeaderType &
HEADER_TYPE_MULTI_FUNCTION) == 0x00)) {
break;
}
Thank you
Yao Jiewen
> -----Original Message-----
> From: Ni, Ruiyu
> Sent: Thursday, September 13, 2018 11:11 AM
> To: Zeng, Star <star.z...@intel.com>; edk2-devel@lists.01.org
> Cc: Chang, Tomson <tomson.ch...@intel.com>; Yao, Jiewen
> <jiewen....@intel.com>; Huang, Jenny <jenny.hu...@intel.com>; Chan,
> Amy <amy.c...@intel.com>
> Subject: Re: [edk2] [PATCH] IntelSiliconPkg IntelVTdDxe: Optimize when func
> 0 is not implemented
>
> On 9/13/2018 10:10 AM, Star Zeng wrote:
> > REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1169
> >
> > PCI spec:
> > They are also required to always implement function 0 in the device.
> > Implementing other functions is optional and may be assigned in any
> > order (i.e., a two-function device must respond to function 0 but
> > can choose any of the other possible function numbers (1-7) for the
> > second function).
> >
> > This patch updates ScanPciBus() to not scan other functions if
> > function 0 is not implemented.
> >
> > Test done:
> > Added debug code below in the second loop of ScanPciBus(),
> > compared the debug logs with and without this patch, many
> > non-0 unimplemented functions are skipped correctly.
> >
> > DEBUG ((
> > DEBUG_INFO,
> > "%a() B%02xD%02xF%02x VendorId: %04x DeviceId: %04x\n",
> > __FUNCTION__,
> > Bus,
> > Device,
> > Function,
> > VendorID,
> > DeviceID
> > ));
> >
> > Cc: Jiewen Yao <jiewen....@intel.com>
> > Cc: Rangasai V Chaganty <rangasai.v.chaga...@intel.com>
> > Cc: Tomson Chang <tomson.ch...@intel.com>
> > Cc: Jenny Huang <jenny.hu...@intel.com>
> > Cc: Amy Chan <amy.c...@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Star Zeng <star.z...@intel.com>
> > ---
> > IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
> b/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
> > index 36750b3f1d9c..305995de032c 100644
> > --- a/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
> > +++ b/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
> > @@ -1,6 +1,6 @@
> > /** @file
> >
> > - Copyright (c) 2017, Intel Corporation. All rights reserved.<BR>
> > + Copyright (c) 2017 - 2018, Intel Corporation. All rights reserved.<BR>
> > This program and the accompanying materials
> > are licensed and made available under the terms and conditions of
> the BSD License
> > which accompanies this distribution. The full text of the license may
> be found at
> > @@ -247,6 +247,12 @@ ScanPciBus (
> > VendorID = PciSegmentRead16
> (PCI_SEGMENT_LIB_ADDRESS(Segment, Bus, Device, Function,
> PCI_VENDOR_ID_OFFSET));
> > DeviceID = PciSegmentRead16
> (PCI_SEGMENT_LIB_ADDRESS(Segment, Bus, Device, Function,
> PCI_DEVICE_ID_OFFSET));
> > if (VendorID == 0xFFFF && DeviceID == 0xFFFF) {
> > + if (Function == 0) {
> > + //
> > + // If function 0 is not implemented, do not scan other
> functions.
> > + //
> > + break;
> > + }
> > continue;
> > }
> >
> >
> Reviewed-by: Ruiyu Ni <ruiyu...@intel.com>
>
> --
> Thanks,
> Ray
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