Segher Boessenkool wrote:
The proposed use clearly would treat them as generic, since in the
context of the Xilinx UART they're just not needed -- it's known
beforehand and most probably fixed how/where the registers are mapped.
There's just no need for such info in the device tree -- unless you're
going to teach the *generic* driver to handle this specific (and
possibly others alike) kind of a device.
I was under the impression that the "xilinx uart" was just a 16550 (or so)
with its registers wired up in a slightly unusual way. If it's a
completely
different device, of course you need a separate binding, and you might not
want reg-shift properties etc. there.
It seems to be 16550 in the core, although coming in many flavors. :-)
"reg-*" has nothing to do with Linux device driver implementation
issues: it describes how a device is physically wired up!
Hm... wasn't that you who were telling that use of "range"
properties guarantees 1:1 correspondence of the upstream/downstream
bus addresses (in their LSB part of course -- meaning that the device
registers 0..x are seen by the CPU at addresses base+0..base+X?
I have no idea what "ranges" has to do with this.
Me neither. :-)
This device is not a memory-mapped bus, it's a UART.
IIRC, we were discussing MTD then, with an imaginary (for PPC) case of it
being reverse-endian (actually happened on other archs)... IMHO, how the child
bus addresses correspond to parent's one 1:1, doesn't imply that you can't
have a device wired to the child bus a strange way, e.g. with byte-enables
"reversed"...
In support of my argument; the fact that you need a table of data says
to me that this data should really be encoded in the device tree. :-)
Not at all.
Not _necessarily_. I agree with Grant here: for many of these devices
with byte-size registers, it is very common to find them with their
register banks wired up differently, and that is often the *only*
difference to the "normal" device. In this situation, it makes a lot
of sense to describe that difference with "reg-*" properties.
Note that "compicated" mapping is not (necessarily) a property of
the device itself but generally a property of the chip select circuit,
i.e. external entity.
There is no difference insofar as the device tree is concerned.
OK...
Segher
WBR, Sergei
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