DT vs ARM static mappings
Pawel Moll
pawel.moll at arm.com
Wed Sep 21 05:41:49 EDT 2011
> > 2. Single DT_MACHINE_START matching (the most generic) "arm,vexpress"
> > and doing (rougly) this in v2m_map_io:
> >
> > of_scan_flat_dt(v2m_dt_iotable_init, NULL);
> >
> > v2m_dt_iotable_init(...)
> > {
> > if (depth != 0)
> > return 0;
> > if (of_flat_dt_is_compatible(node, "arm,vexpress-legacy"))
> > iotable_init(v2m_io_desc_legacy);
> > else (of_flat_dt_is_compatible(node, "arm,vexpress-rs1"))
> > iotable_init(v2m_io_desc_rs1);
> > else
> > panic();
> > }
> >
> > Neither of them seem particularly appealing... ;-)
>
> But I think both ways would be acceptable in the end. It's not a lot
> of extra code either way. In the second case, I would probably have
> the legacy case as a special variant of the map_io function and have
> all others be the default instead of falling back to panic though.
Ok, I'll go (roughly) that way.
> > In my case it's sysreg and sysctl. There are two more users of static
> > mappings: timer01 and timer23, but they could at some point do ioremap()
> > on their own (especially with Nico's changes).
>
> Well, I think with Nico's cahnges, you /can/ actually do ioremap for
> areas that have been mapped through the iotable before kmalloc is up.
> IIRC, omap does this for a number of peripherals.
>
> It's a bit of a hack, but I think it's much better than taking hardcoded
> addresses.
Yes, I was thinking about that last night. If you think it's acceptable
I'll do this (killing MMIO_P2V on the way ;-)
> With the combination of the points mentioned above, you should be
> able to do:
>
> - map the entire I/O area in map_io(), depending on the board
> - have an __iomem pointer for the sysreg
> - populate that pointer using of_iomap from the device tree address
> before you first access it.
>
> Do you think that would work?
Yes, I suppose so. The last bit (getting the offset from DT) will be a
little ugly, I think, but let's wait till I get some code done.
Cheers!
Paweł
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