Re: [RFC v4 1/3] MdeModulePkg/PciHostBridgeDxe: Add support for address translation

[Guo Heyi <heyi.guo@linaro.org>]

On Wed, Feb 28, 2018 at 10:39:24AM +0100, Laszlo Ersek wrote:
> On 02/28/18 08:53, Guo Heyi wrote:
> > On Wed, Feb 28, 2018 at 03:25:03PM +0800, Ni, Ruiyu wrote:
> 
> >> Heyi,
> >> My understanding is this whole change is backward compatible.
> >> Which means an old version of PciHostBridgeLib + new PciHostBridgeLib.h +
> >> new PciHostBridgeDxe driver won't cause build failure.
> >> right?
> > 
> > Not really; as Laszlo indicated in one mail, some implementations of
> > PciHostBridgeLib uses temporary PCI_ROOT_BRIDGE_APERTURE variables and only
> > initialize Base and Limit fields of the variables, like the code in
> > https://github.com/tianocore/edk2/blob/master/CorebootPayloadPkg/Library/PciHostBridgeLib/PciHostBridgeSupport.c#L315
> > and
> > https://github.com/tianocore/edk2/blob/master/OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c#L216
> > and
> > https://github.com/tianocore/edk2/blob/master/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c#L189
> 
> Right -- while Ray is asking whether this change can cause a build
> failure (and no, it can't), it is true that some PciHostBridgeLib
> instances don't fully clear some structures that "PciHostBridgeLib.h"
> defines (only member-wise assignments exist). So client code has to be
> patched up for functionality, not for build errors.
> 
> > I'm also preparing the patches for these PciHostBridgeLib instances in edk2
> > tree, which are expected to be committed after PciHostBridgeLib.h change and
> > before PciHostBridge driver change.
> 
> That's a great idea; it should help with bisectability.
> 
> In fact, you could submit those patches first (even independently); I
> think they'd mostly just insert a few well-placed ZeroMem() calls. One
> could argue that they should have been added right from the start (we
> expected the "PciHostBridgeLib.h" structures to expand over time, just
> missed a few init spots for them).

That's a good idea. I'll do that.

Thanks,
Heyi

> 
> Thanks,
> Laszlo