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[PATCH] fixup for pci config_access on alchemy au1x000

To: linux-mips@linux-mips.org
Subject: [PATCH] fixup for pci config_access on alchemy au1x000
From: Alexander Bigga <ab@mycable.de>
Date: Tue, 29 Aug 2006 16:48:34 +0200
Cc: ppopov@embeddedalley.com
Organization: mycable GmbH
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: KMail/1.7.2
Hi all,

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?

Thanks a lot for your comments!

Best regard,


Alexander

--- linux-2.6.18-rc5/arch/mips/pci/ops-au1000.c 2006-08-28 12:09:15.000000000 
+0200
+++ linux-2.6.18-rc5-dev/arch/mips/pci/ops-au1000.c     2006-08-29 
13:08:59.000000000 +0200
@@ -110,7 +110,7 @@
        if (first_cfg) {
                /* reserve a wired entry for pci config accesses */
                first_cfg = 0;
-               pci_cfg_vm = get_vm_area(0x2000, 0);
+               pci_cfg_vm = get_vm_area(0x2000, VM_IOREMAP);
                if (!pci_cfg_vm)
                        panic (KERN_ERR "PCI unable to get vm area\n");
                pci_cfg_wired_entry = read_c0_wired();

-- 
Alexander Bigga     Tel: +49 4873 90 10 866
mycable GmbH        Fax: +49 4873 901 976
Boeker Stieg 43
D-24613 Aukrug      eMail: ab@mycable.de


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