Subject: Re: freeze when reading a PCI bridge register

From: Nicolas Lavocat <[email-masked]>
Date: Wed, 22 Apr 2009 11:26:26 +0200

In fact, because system froze, I wanted to know where was the problem,
so, step by step, I removed operations, until try to  read this
register, basic operation when a PCI device is used. This register can
be read with JTAG, and under uboot, so I think that it is not a PCI
problem..

Nicolas Lavocat

tiejun.chen a écrit :

Nicolas Lavocat wrote:

Hi everybody!

I' am trying to configure a PCI bridge on a private board, with a
powerpc . In a first time, I tried to get informations about PCI
devices, in order to be sure that my read and write methods work (
using 2 configuration registers, like on an x86 architecture.) . 2
configuration registers are used, for example we write an encoded
address (it is a request to a PCI device) in the first and the answer of
the PCI device can be read in the second register (it is a configuration
cycle)
Firstly, I did it by JTAG: it works. Then, under uboot, it is ok.

For example, the code used under u-boot:

volatile u32* addr;
u32 vendor_device_ID;

puts("PCI1 reading PCI VENDOR and DEVICE ID\n");
addr=CFG_ADDR_PCI1;
*addr=0x80007800;

addr= CFG_DATA_PCI1;
vendor_device_ID= *addr;
printf("PCI1: PCI1_VENDOR_DEVICE_ID= %08x \n" ,vendor_device_ID);

Therefore, when I do the same thing under Linux, the system crash when I
try to read the second register...
Linux is frozen, and there is no error message.
Under Linux, I made an ioremap before use the registers and access to
these registers thanks to functions "in_be32" and "out_be32".
I tried with different endianness to avoid an error of this type.

If I understand, the main difference between u-boot and Linux (about
registers access) is the activation of the MMU.
So I thought that problem could come from it. I think the problem could
came from the configuration of DBAT and IBATS registers of the MMU, but
I didn't found any information about the MMU configuration under Linux.
So after this novel, I have some questions:

-Is the MMU configuration generic under Linux?
-Does somebody think that the problem doesn't come from MMU?
-How does work ioremap? Is it a fully software function, or does it
speaks to MMU to get the effective address from physical address?
-Does somebody have an idea, or a documentation about MMU configuration
under linux?
-Do you think that my MMU is under the control of an evil spirit? ^^

thank you for your help

Looks you want to re-configure the PCI bridge again?

If so you really should do the private fixup function via some kernel API,
DECLARE_PCI_FIXUP_XXXX. It's not reasonable to re-configure PCI bridge after PCI
sub-system initial process is completed by kernel.

Best Regards
Tiejun

Nicolas Lavocat
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