Hello.
Alexander Bigga wrote:
I've encountered a serious problem with PCI config space access on Au1x000
platforms with recent 2.6.x-kernel. With 2.4.31 the same hardware works fine.
So I was looking for the differences:
Symptoms:
- no PCI-device is seen on bootup though two or three cards are present
- lspci output is empty
- OR: lspci shows 20 times the same device
(- OR: in some slot-configurations it worked anyhow)
System(s):
1. platform with Au1500 and three PCI-devices (actually a mycable XXS1500
with backplane for three PCI-devices)
2. platform with Au1550 and two PCI-devices (custom board)
Debugging:
I digged down to the config_access() of the au1xxx-processors in
arch/mips/pci/ops-au1000.c and switched on DEBUG.
The code of config_access() seems to be almost the same as of the
2.4.x-kernel. But the "pci_cfg_vm->addr" returned by get_vm_area(0x2000, 0)
once on booting is different. That's of course not forbidden. But the
alignment seems to be wrong. In my case, I received:
2.4.31: pci_cfg_vm->addr = c0000000
2.6.18-rc5: pci_cfg_vm->addr = c0101000
To make it short: With 2.6.x it fails on the first config-access with:
"PCI ERR detected: status 83a00356".
Fixup:
My fix is now, to use the VM_IOREMAP-flag in the get_vm_area call. This flag
seems to be introduced in mm/vmalloc.c a long time ago (in 2.6.7-bk13, I
found in gitweb).
Now, the returned address is pci_cfg_vm->addr = c0104000 and everything works
fine.
What do you think about my fixup-patch?
Nobody's using the get_vm_area()-call without any flag ("0"). Was it only
forgotten in the arch/mips/pci/ops-au1000.c?
Or am I completely wrong?
You're correct -- this code was only working by some chance. Once you get
a virtual address not aligned to 8K, it breaks completely since the pages
can't constitute a valid pair for wired entry anymore.
Actually, in 2.4 the situation seems to be even worse as get_vm_area()
there has no provision for the address alignment at all!
Best regard,
Alexander
WBR, Sergei
