From 6a744d40d0c707b43202ae9b6a1d6ae89f6f864b Mon Sep 17 00:00:00 2001 From: Laszlo Ersek Date: Sat, 28 Apr 2018 23:22:59 +0200 Subject: OvmfPkg: introduce PciCapPciSegmentLib Add a library class, and a BASE lib instance, that are layered on top of PciCapLib, and allow clients to plug a PciSegmentLib backend into PciCapLib, for config space access. (Side note: The "MaxDomain" parameter is provided because, in practice, platforms exist where a PCI Express device may show up on a root bridge such that the root bridge doesn't support access to extended config space. Earlier the same issue was handled for MdeModulePkg/PciHostBridgeDxe in commit 014b472053ae3. However, that solution does not apply to the PciSegmentLib class, because: (1) The config space accessor functions of the PciSegmentLib class, such as PciSegmentReadBuffer(), have no way of informing the caller whether access to extended config space actually succeeds. (For example, in the UefiPciSegmentLibPciRootBridgeIo instace, which could in theory benefit from commit 014b472053ae3, the EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL.Pci.Read() status code is explicitly ignored, because there's no way for the lib instance to propagate it to the PciSegmentLib caller. If the EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL.Pci.Read() call fails, then DxePciSegmentLibPciRootBridgeIoReadWorker() returns Data with indeterminate value.) (2) There is no *general* way for any firmware platform to provide, or use, a PciSegmentLib instance in which access to extended config space always succeeds. In brief, on a platform where config space may be limited to 256 bytes, access to extended config space through PciSegmentLib may invoke undefined behavior; therefore PciCapPciSegmentLib must give platforms a way to prevent such access.) Cc: Ard Biesheuvel Cc: Jordan Justen Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Laszlo Ersek Reviewed-by: Ard Biesheuvel --- OvmfPkg/OvmfPkg.dec | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'OvmfPkg/OvmfPkg.dec') diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec index 74818a2e2a..fbec1cfe4a 100644 --- a/OvmfPkg/OvmfPkg.dec +++ b/OvmfPkg/OvmfPkg.dec @@ -35,6 +35,11 @@ # config space. PciCapLib|Include/Library/PciCapLib.h + ## @libraryclass Layered on top of PciCapLib, allows clients to plug a + # PciSegmentLib backend into PciCapLib, for config space + # access. + PciCapPciSegmentLib|Include/Library/PciCapPciSegmentLib.h + ## @libraryclass Access QEMU's firmware configuration interface # QemuFwCfgLib|Include/Library/QemuFwCfgLib.h -- cgit v1.2.3