[edk2-platforms][PATCH 1/1] Silicon/Broadcom/Bcm27xx: Allow more than one device on pcie busses >1

["René Treffer" <treffer+groups.io@measite.de>]

There is only a single pcie port on the bcm2711 so limiting the number of
devices to 1 worked as long as there is no way to add a pcie switch.

On the compute module 4 it is possible to add a pcie switch (tested with
asm1184e) which adds 5 new pcie busses.

In the current state the pci enumeration fails for the pcie switch
internal bus (usually bus 2, device 1,3,5,7). The root port gets
configured with
subordniate=0x2 after enumeration. That blocks e.g. linux from discovering
devices behind the switch.

Devices behind the switch work after lifting the device limit on busses
other than 0 and 1.
---
 .../Library/Bcm2711PciSegmentLib/PciSegmentLib.c   | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git
a/Silicon/Broadcom/Bcm27xx/Library/Bcm2711PciSegmentLib/PciSegmentLib.c
b/Silicon/Broadcom/Bcm27xx/Library/Bcm2711PciSegmentLib/PciSegmentLib.c
index 44ce3b4b99..4af9374d23 100644
--- a/Silicon/Broadcom/Bcm27xx/Library/Bcm2711PciSegmentLib/PciSegmentLib.c
+++ b/Silicon/Broadcom/Bcm27xx/Library/Bcm2711PciSegmentLib/PciSegmentLib.c
@@ -78,6 +78,7 @@ PciSegmentLibGetConfigBase (
   UINT64        Base;
   UINT64        Offset;
   UINT32        Dev;
+  UINT32        Bus;
 
   Base = PCIE_REG_BASE;
   Offset = Address & 0xFFF;         /* Pick off the 4k register offset */
@@ -89,17 +90,16 @@ PciSegmentLibGetConfigBase (
     Base += PCIE_EXT_CFG_DATA;
     if (mPciSegmentLastAccess != Address) {
       Dev = EFI_PCI_ADDR_DEV (Address);
+      Bus = EFI_PCI_ADDR_BUS (Address);
       /*
-       * Scan things out directly rather than translating the "bus" to
a device, etc..
-       * only we need to limit each bus to a single device.
+       * There can only be a single device on bus 1 (downstream of root).
+       * Subsequent busses (behind a PCIe switch) could have more.
        */
-      if (Dev < 1) {
-          MmioWrite32 (PCIE_REG_BASE + PCIE_EXT_CFG_INDEX, Address);
-          mPciSegmentLastAccess = Address;
-      } else {
-          mPciSegmentLastAccess = 0;
+      if (Dev > 0 && (Bus == 1 || Bus == 0)) {
           return 0xFFFFFFFF;
       }
+      MmioWrite32 (PCIE_REG_BASE + PCIE_EXT_CFG_INDEX, Address);
+      mPciSegmentLastAccess = Address;
     }
   }
   return Base + Offset;
-- 
2.27.0