[U-Boot] calling pci_init before relocation?

[Michael Schwingen]

Albert ARIBAUD wrote:
> Le 30/01/2011 23:46, Michael Schwingen a écrit :
>> Am 01/30/2011 11:07 PM, schrieb Albert ARIBAUD:
>>> Hi Michael,
>>>
>>> Le 30/01/2011 22:39, Michael Schwingen a écrit :
>>>> Hi,
>>>>
>>>> ist it allowed to call pci_init before relocation?
>>>>
>>>> The code looks like this is not supposed to happen. However, on ARM,
>>>> arm_pci_init (which calls pci_init in turn) is called from
>>>> init_sequence, which happens before relocation.
>>>>
>>>> Am I overlooking some way in which this can actually work? Are there
>>>> boards using this?
>>>>
>>>> If I move pci_init down into board_init_r, I can get PCI working on
>>>> IXP42x, but I am worried if this will cause problems on other boards.
>>> I cannot see a reason why pci_init should not work before relocation as
>>> long as it does not read or write BSS variables or write non-const
>>> initialized data -- or overflow the (admittedly limited) C stack.
>> Because it does just that - from drivers/pci/pci.c:
>>
>> static struct pci_controller* hose_head;
>>
>> void pci_init(void)
>> {
>> [...]
>>      hose_head = NULL;
>>
>>      /* now call board specific pci_init()... */
>>      pci_init_board();
>> }
>>
>> pci_init_board will then call code that ends up calling
>> pci_register_hose, which adds elements into the list at hose_head.
>
> Tough luck -- BTW, how does this code allocate the memory? The heap is 
> obviously not going to work before relocation.
The new hose pointer is passed into that function - the calling code 
would have to either malloc that, or use a static struct (as it is done 
on IXP, because there is only one PCI bus). Both will fail before 
relocation - the hose structure would have to be embedded into the 
global data struct.

>
>>> Are you asking because you discovered that pci_init does not work when
>>> called from board_init_f? If so, did you determine exactly what goes 
>>> wrong?
>> The system hangs during early init, and does not get past relocation.
>>
>> Note that I can only *test* PCI on IXP42x, however, this is common code,
>> so I do not see how this could behave different on other ARM systems.
>>
>> If I interpret the code correct, the PCI code is called from
>> board_init_r on PowerPC platforms.
>
> Hmm... Now let's reverse the question: why should PCI be initialized 
> before relocation? At this point the only goal of the init_board_f 
> code is to get the RAM working for relocation, and the only useful 
> device is the serial console. Does pci_init() help for either RAM or 
> console?
I don't see a reason to do that - my vote would be to do the PCI 
initialization after relocation, but I am not sure if there are any ARM 
boards that need this for whatever reason. If there are any, I would 
expect them to be broken anyway since relocation was added, but I can't 
be sure.

cu
Michael