address translation for PCIe-to-localbus bridge

[Gerlando Falauto]

On 11/12/2013 08:05 AM, Thomas Petazzoni wrote:
> Dear Grant Likely,
>
> On Mon, 11 Nov 2013 15:50:50 +0000, Grant Likely wrote:
>
>>> So the mbus would register an address xlate for its node that is
>>> called instead of ranges parsing. For the example in my last message
>>> the FPGA driver would register an xlate that made addresses relative
>>> to its own BAR0 address.
>>
>> There are already bus-specific transations available. Take a look at
>> struct of_bus in drivers/of/address.c
>
> Hum, right, but unless I'm wrong the of_busses[] array of struct of_bus
> is fixed in drivers/of/address.c, and as it is, there is no way for a
> specific bus driver to provide its own struct of_bus.

That was exactly my understanding as well, and that's where I was 
expecting some trickery to happen.

> So that would need to be extended, right?

The other approach I was foreseeing was to implement a way of 
dynamically updating the DT when the PCI subsystem enumerates the 
devices and assigns memory areas (namely, I would expect the ranges 
property to reflect that). But this would imply a standard way of 
defining the ranges property (I would expect something like <bar# 
start_addr length>, with an arguable number of cells). And I could
not find any such definition in the PCI bus binding document, so I'm 
probably completely off-track here. Aren't I?

After all, we should expect a driver to behave (and expect) the same of 
the DT, regardless of whether enumeration was performed by firmware or
by the OS itself. Or am I wrong on this too?

Thanks guys!
Gerlando