On Thu, Mar 01, 2018 at 11:17:30AM +0100, Laszlo Ersek wrote:
> Hello Heyi,
>
> On 03/01/18 07:57, Heyi Guo wrote:
> > Use ZeroMem to initialize all fields in temporary
> > PCI_ROOT_BRIDGE_APERTURE variables to zero. This is not mandatory but
> > is helpful for future extension: when we add new fields to
> > PCI_ROOT_BRIDGE_APERTURE and the default value of these fields can
> > safely be zero, this code will not suffer from an additional
> > change.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Heyi Guo <heyi....@linaro.org>
> >
> > Cc: Jordan Justen <jordan.l.jus...@intel.com>
> > Cc: Anthony Perard <anthony.per...@citrix.com>
> > Cc: Julien Grall <julien.gr...@linaro.org>
> > Cc: Ruiyu Ni <ruiyu...@intel.com>
> > Cc: Laszlo Ersek <ler...@redhat.com>
> > Cc: Ard Biesheuvel <ard.biesheu...@linaro.org>
> > ---
> > OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c | 4 ++++
> > OvmfPkg/Library/PciHostBridgeLib/XenSupport.c | 5 +++++
> > 2 files changed, 9 insertions(+)
> >
> > diff --git a/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
> > b/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
> > index ff837035caff..4a650a4c6df9 100644
> > --- a/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
> > +++ b/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c
> > @@ -217,6 +217,10 @@ PciHostBridgeGetRootBridges (
> > PCI_ROOT_BRIDGE_APERTURE Mem;
> > PCI_ROOT_BRIDGE_APERTURE MemAbove4G;
> >
> > + ZeroMem (&Io, sizeof (Io));
> > + ZeroMem (&Mem, sizeof (Mem));
> > + ZeroMem (&MemAbove4G, sizeof (MemAbove4G));
> > +
> > if (PcdGetBool (PcdPciDisableBusEnumeration)) {
> > return ScanForRootBridges (Count);
> > }
>
> This is OK. (Although for a trivial perf improvement, you could move the
> ZeroMem() calls after the PcdGetBool() / return. Not necessary, up to
> you.)
>
> However:
>
> > diff --git a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
> > b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
> > index 31c63ae19e0a..aaf101dfcb0e 100644
> > --- a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
> > +++ b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
> > @@ -193,6 +193,11 @@ ScanForRootBridges (
> >
> > *NumberOfRootBridges = 0;
> > RootBridges = NULL;
> > + ZeroMem (&Io, sizeof (Io));
> > + ZeroMem (&Mem, sizeof (Mem));
> > + ZeroMem (&MemAbove4G, sizeof (MemAbove4G));
> > + ZeroMem (&PMem, sizeof (PMem));
> > + ZeroMem (&PMemAbove4G, sizeof (PMemAbove4G));
> >
> > //
> > // After scanning all the PCI devices on the PCI root bridge's primary
> > bus,
> >
>
> these ZeroMem() calls are not in the correct place. Please move them
> into the "PrimaryBus" loop just underneath. That loop works like this:
>
> For each primary bus:
>
> (1) set all of the aperture variables to "nonexistent":
>
> Io.Base = Mem.Base = MemAbove4G.Base = PMem.Base = PMemAbove4G.Base =
> MAX_UINT64;
> Io.Limit = Mem.Limit = MemAbove4G.Limit = PMem.Limit = PMemAbove4G.Limit
> = 0;
>
> (2) accumulate the BARs of the devices on the bus into the aperture
> variables
>
> (3) call InitRootBridge() with the aperture variables
>
>
> That is, the ZeroMem() calls that you are adding have to be part of step
> (1). So, please replace the assignments
>
> Io.Base = Mem.Base = MemAbove4G.Base = PMem.Base = PMemAbove4G.Base =
> MAX_UINT64;
> Io.Limit = Mem.Limit = MemAbove4G.Limit = PMem.Limit = PMemAbove4G.Limit
> = 0;
>
> with
>
> ZeroMem (&Io, sizeof (Io));
> ZeroMem (&Mem, sizeof (Mem));
> ZeroMem (&MemAbove4G, sizeof (MemAbove4G));
> ZeroMem (&PMem, sizeof (PMem));
> ZeroMem (&PMemAbove4G, sizeof (PMemAbove4G));
> Io.Base = Mem.Base = MemAbove4G.Base = PMem.Base = PMemAbove4G.Base =
> MAX_UINT64;
Will it cause functional issue?
My idea of making the change is like this:
1. ZeroMem() is used to initialize all fields of APERTURE to 0; it can make it
in the current place of the patch;
2. In the loop, some fields may be changed by the end of each iteration, and it
is the responsibility of the existing code to re-initialize the changed
fields
to expected values explicitly. It seems not necessary to re-initialize the
other
fields which will not be changed.
However, your advice may be better that merges the initialization code together.
I can make the change in the next version of patch.
Thanks,
Heyi
>
> Thanks!
> Laszlo
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