Re: [edk2-devel] [PATCH V2] MdePkg-PciExpress40.h: DVSEC definition missing

["Ni, Ray" <ray.ni@intel.com>]

I agree with you about that fact😊

These "[1]" was added 6 years ago when "[0]" still caused compilation failure.
Later, about 5 years ago,  Mike enabled "[0]" with the below change in MdePkg/Include/Base.h:

//
// Disable warning when last field of data structure is a zero sized array.
//
#pragma warning ( disable : 4200 )


We cannot change these "[1]" to "[0]" because that would cause existing code that depends on
sizeof() result fails.
But for new code, it's encouraged to use "[0]".

Thanks,
Ray


> -----Original Message-----
> From: Javeed, Ashraf <ashraf.javeed@intel.com>
> Sent: Thursday, March 19, 2020 6:00 PM
> To: Ni, Ray <ray.ni@intel.com>; Gao, Liming <liming.gao@intel.com>; Liu, Zhiguang <zhiguang.liu@intel.com>; Kinney,
> Michael D <michael.d.kinney@intel.com>
> Cc: devel@edk2.groups.io
> Subject: RE: [edk2-devel] [PATCH V2] MdePkg-PciExpress40.h: DVSEC definition missing
> 
> All the PCIe capability structures with the PCI_EXPRESS_EXTENDED_CAPABILITIES_HEADER; that has variable length
> features have been implemented in this way. I am counting around 12 structures which have been defined in the same
> way.
> 
> > -----Original Message-----
> > From: Ni, Ray <ray.ni@intel.com>
> > Sent: Thursday, March 19, 2020 2:30 PM
> > To: Javeed, Ashraf <ashraf.javeed@intel.com>; Gao, Liming
> > <liming.gao@intel.com>; Liu, Zhiguang <zhiguang.liu@intel.com>; Kinney,
> > Michael D <michael.d.kinney@intel.com>
> > Cc: devel@edk2.groups.io
> > Subject: RE: [edk2-devel] [PATCH V2] MdePkg-PciExpress40.h: DVSEC
> > definition missing
> >
> > I am sorry I just noticed this patch.
> > Is it better to have "DesignatedVendorSpecific[0]"?
> > This will make the sizeof (structure) more accurate.
> >
> > > -----Original Message-----
> > > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of
> > Javeed,
> > > Ashraf
> > > Sent: Tuesday, March 17, 2020 4:04 PM
> > > To: devel@edk2.groups.io
> > > Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming
> > > <liming.gao@intel.com>; Liu, Zhiguang <zhiguang.liu@intel.com>
> > > Subject: [edk2-devel] [PATCH V2] MdePkg-PciExpress40.h: DVSEC
> > > definition missing
> > >
> > > BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2598
> > >
> > > All registers definition of DVSEC are defined as per the PCI Express
> > > Base Specification 4.0 chapter 7.9.6.
> > >
> > > Signed-off-by: Ashraf Javeed <ashraf.javeed@intel.com>
> > > Cc: Michael D Kinney <michael.d.kinney@intel.com>
> > > Cc: Liming Gao <liming.gao@intel.com>
> > > Cc: Zhiguang Liu <zhiguang.liu@intel.com>
> > >
> > > V2: fixed the comment section description for DVSEC definitions
> > > ---
> > >  MdePkg/Include/IndustryStandard/PciExpress40.h | 28
> > > ++++++++++++++++++++++++++++
> > >  1 file changed, 28 insertions(+)
> > >
> > > diff --git a/MdePkg/Include/IndustryStandard/PciExpress40.h
> > > b/MdePkg/Include/IndustryStandard/PciExpress40.h
> > > index 9d9b272546..0564d72861 100644
> > > --- a/MdePkg/Include/IndustryStandard/PciExpress40.h
> > > +++ b/MdePkg/Include/IndustryStandard/PciExpress40.h
> > > @@ -4,6 +4,7 @@ Support for the PCI Express 4.0 standard.
> > >  This header file may not define all structures.  Please extend as required.
> > >
> > >  Copyright (c) 2018, American Megatrends, Inc. All rights
> > > reserved.<BR>
> > > +Copyright (c) 2020, Intel Corporation. All rights reserved.<BR>
> > >  SPDX-License-Identifier: BSD-2-Clause-Patent
> > >
> > >  **/
> > > @@ -78,6 +79,33 @@ typedef struct {
> > >  } PCI_EXPRESS_EXTENDED_CAPABILITIES_PHYSICAL_LAYER_16_0;
> > >  ///@}
> > >
> > > +/// The Designated Vendor Specific Capability definitions /// Based
> > > +on section 7.9.6 of PCI Express Base Specification 4.0.
> > > +///@{
> > > +typedef union {
> > > +  struct {
> > > +    UINT32 DvsecVendorId                                        : 16; //bit 0..15
> > > +    UINT32 DvsecRevision                                        : 4;  //bit 16..19
> > > +    UINT32 DvsecLength                                          : 12; //bit 20..31
> > > +  }Bits;
> > > +  UINT32                                                        Uint32;
> > > +}PCI_EXPRESS_DESIGNATED_VENDOR_SPECIFIC_HEADER_1;
> > > +
> > > +typedef union {
> > > +  struct {
> > > +    UINT16 DvsecId                                              : 16; //bit 0..15
> > > +  }Bits;
> > > +  UINT16                                                        Uint16;
> > > +}PCI_EXPRESS_DESIGNATED_VENDOR_SPECIFIC_HEADER_2;
> > > +
> > > +typedef struct {
> > > +  PCI_EXPRESS_EXTENDED_CAPABILITIES_HEADER                      Header;
> > > +  PCI_EXPRESS_DESIGNATED_VENDOR_SPECIFIC_HEADER_1
> > > DesignatedVendorSpecificHeader1;
> > > +  PCI_EXPRESS_DESIGNATED_VENDOR_SPECIFIC_HEADER_2
> > > DesignatedVendorSpecificHeader2;
> > > +  UINT8                                                         DesignatedVendorSpecific[1];
> > >
> > +}PCI_EXPRESS_EXTENDED_CAPABILITIES_DESIGNATED_VENDOR_SPECIFIC;
> > > +///@}
> > > +
> > >  #pragma pack()
> > >
> > >  #endif
> > > --
> > > 2.21.0.windows.1
> > >
> > >
> > >