Re: [PATCH 2/3] [POWERPC] Xilinx: of_serial support for Xilinx uart 16550.

["Grant Likely" <grant.likely@secretlab.ca>]

On Fri, Mar 21, 2008 at 7:00 AM, Sergei Shtylyov
<sshtylyov@ru.mvista.com> wrote:
>  Grant Likely wrote:
>  > Personally, I'm not fond of this approach.  There is already some
>  > traction to using the reg-shift property to specify spacing, and I
>  > think it would be appropriate to also define a reg-offset property to
>  > handle the +3 offset and then let the xilinx 16550 nodes use those.
>
>     That's making things only worse than the mere "reg-shift" idea. I think
>  that both are totally wrong. Everything about the programming interface should
>  be said in the "compatible" and possibly "model" properties. of_serial driver
>  should recognize them and pass the necessary details to 8250.c. As for me, I'm
>  strongly against plaguing the device tree with the *Linux driver
>  implementation specifics* (despite I was trying this with MTD -- there it
>  seemed somewhat more grounded :-).

Not true.  Compatible defines what the node is describing.  It is
perfectly valid for a compatible value definition to also defines some
additional properties that can be queried for interface details.
Xilinx is completely free to define a "xlnx,..." compatible value for
their ns16550 compatible device.  However, 'sparse' ns16550 devices
are a common and well known variation so I think it is valid and
reasonable to define a compatible binding for this case.

As for using a new binding like "sparse16550" instead of extending
"ns16550"; it is because reg-shift and reg-offset would be required
nodes and therefore is not compatible with drivers using the original
ns16550 binding.  Using a new namespace gives freedom to define the
required properties.

Cheers,
g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.