[PATCH] fixup for pci config_access on alchemy au1x000

[PATCH] fixup for pci config_access on alchemy au1x000

[Alexander Bigga]

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

Re: [PATCH] fixup for pci config_access on alchemy au1x000

[Ralf Baechle]

On Tue, Aug 29, 2006 at 04:48:34PM +0200, Alexander Bigga wrote:

> 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!

The patch looks ok, so just the usual technicalities:

 - Please include a Signed-off-by: line.
 - Don't use a bloody crapmailer that garbles patches into some sort of
   ASCII spinach.

  Ralf

Re: [PATCH] fixup for pci config_access on alchemy au1x000

[Alexander Bigga]

Thanks for applying.

On Tue, Aug 29, 2006 at 04:56:07PM +0100, Ralf Baechle wrote:
> The patch looks ok, so just the usual technicalities:
> 
>  - Please include a Signed-off-by: line.

Ok. Will do this in future. 

>  - Don't use a bloody crapmailer that garbles patches into some sort of
>    ASCII spinach.

I'm really sorry. I don't like spinach too ;-)
For future mailings and patches, I will take mutt again.

Alexander
-- 
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

Re: [PATCH] fixup for pci config_access on alchemy au1x000

[Sergei Shtylyov]

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