Hi Thierry,
thanks again for your patience!
On 11/06/2013 01:23 PM, Thierry Reding wrote:
On Wed, Nov 06, 2013 at 11:27:15AM +0100, Gerlando Falauto wrote:
Hi everyone,
I am currently trying to describe an external device within a device
tree in a Kirkwood design.
Such device is accessed through a local (parallel) bus. Since
Kirkwood does not provide such an interface, we added a custom FPGA
(PCIe device) which implements a PCIe-to-localbus bridge.
So essentially BAR0 provides the configuration space for such a
bridge, and BAR1 provides a remapped area where accesses to the
localbus can be performed. BAR2 and BAR3 provide other functions.
So with the appropriate reg encoding of the PCI device, the PCI
driver for the FPGA will automatically get an of_node.
My question is: is there any way I can describe this external device
(I believe as a child node of the PCI device), so that a call to
of_address_to_resource() (or equivalent) from its driver will
automatically translate a localbus address (e.g. 0x0000abcd) to
whatever address was assigned to BAR1 (in my case 0xe0000000 ->
0xe000abcd)?
Perhaps I don't understand properly, but what good is the local bus
address to any driver? I mean you'll have to have a PCI driver to bind
to the PCI device, right?
Correct, and that's the PCI driver for the FPGA, which is (among other
things) a PCI-to-localbus bridge.
> And that PCI driver will only need to obtain
the register addresses from BAR1,
Correct.
then access that region.
That's not 100% right. The PCI driver will only _provide_ the region for
BAR1 (as it is a bridge), not _access_ it.
Why would you need to have it translated via DT?
Because it would be a *separate* driver, the one handling the /external/
"slave" device, to use that region.
In principle, if I wanted to reuse that same external device on a
completely different architecture (which *does* natively provide a
localbus) I should be able to move that same device node together with
its driver. Provided the node is under the right bus, and translation is
configured properly in the device tree, it should then work out of the
box. Or am I completely mistaken?
What I did now (and it works) was to put the device node for the
external device right under the main bus,
/ {
...
ocp@f1000000 {
slave@0,0 {
...
compatible = "keymile,slave";
reg = <0xe0000000 0x200>;
};
};
};
where "0xe0000000" is hardcoded, being the result of the dynamic assignment:
pci 0000:01:00.0: BAR 1: assigned [mem 0xe0000000-0xe7ffffff]
I'd like to avoid that, saying "slave@0,0 is accessible through the
memory area 0x0-0x200 within BAR1 of device 0 on bus 1".
Thanks again,
Gerlando
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