[RFC] PCI: skip pci host bridge as early as possible

[Antony Pavlov]

The barebox' pci_scan_bus() function first tries to setup GT64120
host bridge BARs but fails:

    barebox:/ dmesg
    pci: pci_scan_bus for bus 0
    pci:  last_io = 0x18000000, last_mem = 0x10000000, last_mem_pref = 0x00000000
    pci: class = 00000600, hdr_type = 00000000
    pci: 00:00 [11ab:4620]
    pci: pbar0: mask=00000008 NP memory 0 bytes
    pci: pbar1: mask=01000008 NP memory -16777216 bytes
    pci: pbar2: mask=1c000000 NP memory -469762048 bytes
    pci: BAR does not fit within bus np-mem res
    pci: skip pci host bridge

so PCI host bridge and all discovered devices are misconfigured, e.g.
miitool can't find rtl8139 emulated NIC tranceiver:

    rtl8139_eth pci-10ec:8139.0: rtl8139 (rev 20) at 90: 0200 (base=8f000000)
    rtl8139_eth pci-10ec:8139.0: enabling bus mastering
    ...
    barebox:/ miitool
    miibus0: registered phy as /dev/phy0
    phy0: eth0:   No MII transceiver present!.

Here is linux-3.19 GT64120 host bridge discovery log:

    PCI host bridge to bus 0000:00
    pci_bus 0000:00: root bus resource [mem 0x10000000-0x17ffffff]
    pci_bus 0000:00: root bus resource [io  0x1000-0x1fffff]
    pci_bus 0000:00: No busn resource found for root bus, will use [bus 00-ff]
    pci 0000:00:00.0: [Firmware Bug]: reg 0x14: invalid BAR (can't size)
    pci 0000:00:00.0: [Firmware Bug]: reg 0x18: invalid BAR (can't size)
    pci 0000:00:00.0: [Firmware Bug]: reg 0x1c: invalid BAR (can't size)
    pci 0000:00:00.0: [Firmware Bug]: reg 0x20: invalid BAR (can't size)
    pci 0000:00:00.0: [Firmware Bug]: reg 0x24: invalid BAR (can't size)

The appropriate lspci -v log:

    00:00.0 Host bridge: Marvell Technology Group Ltd. GT-64120/64120A/64121A System Controller (rev 10)
            Subsystem: Red Hat, Inc Device 1100
            Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
            Status: Cap- 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
            Interrupt: pin A routed to IRQ 0
            Subsystem: Red Hat, Inc Device 1100
            Flags: medium devsel
            Memory at <unassigned> (32-bit, prefetchable) [disabled]
            Memory at <ignored> (32-bit, prefetchable) [disabled]
            Memory at <ignored> (32-bit, non-prefetchable) [disabled]
            Memory at <ignored> (32-bit, non-prefetchable) [disabled]
            Memory at <ignored> (32-bit, non-prefetchable) [disabled]
            I/O ports at <ignored> [disabled]

It looks like qemu-system-mips does not fully emulates GT64120 host
bridge BARs so skipping host bridge BAR's setup fixes qemu-malta
problem. But can we skip host bridge BAR's setup for other targets?

Signed-off-by: Antony Pavlov <antonynpavlov at gmail.com>
---
 drivers/pci/pci.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 3a0e7a5..7953c55 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -331,6 +331,11 @@ unsigned int pci_scan_bus(struct pci_bus *bus)
 		pr_debug("%02x:%02x [%04x:%04x]\n", bus->number, dev->devfn,
 		    dev->vendor, dev->device);
 
+		if (class == PCI_CLASS_BRIDGE_HOST) {
+			pr_debug("skip pci host bridge\n");
+			continue;
+		}
+
 		switch (hdr_type & 0x7f) {
 		case PCI_HEADER_TYPE_NORMAL:
 			if (class == PCI_CLASS_BRIDGE_PCI)
@@ -391,11 +396,6 @@ unsigned int pci_scan_bus(struct pci_bus *bus)
 			       bus->number, dev->devfn, dev->vendor, dev->device, class, hdr_type);
 			continue;
 		}
-
-		if (class == PCI_CLASS_BRIDGE_HOST) {
-			pr_debug("skip pci host bridge\n");
-			continue;
-		}
 	}
 
 	/*
-- 
2.1.4