freeze when reading a PCI bridge register

[Liu Dave-R63238]

> 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? ^^
> 
What is the PowerPC you are using?