Hi Mark,
On Saturday 10 August 2013 07:53 PM, Mark Rutland wrote:
+ mac: ethernet@4a100000 {
+ compatible = "ti,am4372-cpsw","ti,cpsw";
One point worth mentioning is that the "ti,am4372-cpsw" string isn't
documented. Will the "ti,am4372-cpsw" binding definitely be a superset
of the "ti,cpsw" binding, and if you were to take the DT as of this
patch, and attempt to use it with a future kernel, can you guarantee
it'll work?
"ti,am4372-cpsw" was not documented as OMAP DT maintainer didn't prefer
documenting only for a new compatible.
For the only patch on this file that went into mainline, in that series
actually I had posted patches to document "ti,am4372-*", but as
maintainer didn't agree, it was discarded [A].
Regarding whether "ti,am4372-cpsw" would be a superset of "ti,cpsw",
information I have (am4372 is in pre silicon stage) is that it is a
reuse from am335x ("ti,cpsw" should have been named "ti,am3352-cpsw" or
something like that, but nothing can be done now) with minor changes and
all existing functionalities available, Mugunthan can shed more light on
this, Mugunthan ?
As mentioned at other places in the thread, for cpsw, only a few
properties to prevent hwmod code crash was added. I am sure that
currently added properties for cpsw will not make driver functional this
Kernel version (if this goes in) or future versions. To make driver work
additional properties are required.
There are many other parameters which are missed here.
Reason has been mentioned in the commit message, quoting relevant here
again,
Actually, as you've marked the nodes disabled, it's probably fine. But
worth considering as properties are added...
There were two factors that was considered while adding cpsw node
1. DT as an ABI
2. While adding DT node, whether all existing required properties has to
be added
Regarding 1 - DT would not make driver work for this Kernel version and
also for not any newer Kernel version, I believe this does not go
against DT an an ABI, although in a negative sense. To make driver work
more DT properties would have to be added.
Regarding 2 - Currently, I believe most required & optional properties
in bindings are defined w.r.t driver (bringing in a Linux attachment).
If DT is only a hardware description, required & optional properties
should correspond to something that are a must for hardware to work and
additional features that can be used respectively. In that sense
interrupts property for many of the peripherals would have to be
considered optional, as it is possible to work in polling mode. And
would it be practical for DT in most of the cases to be a complete
hardware description ?, as to completely describe hardware, we may need
to have a large amount of properties that may not be relevant to
software. If requirement is only that DT should describe hardware that
is relevant for software (this would bring in a software dependency for
DT), required property for one software may not be required for another
piece of software or may be an optional property (like in the case of
interrupts as explained above).
So conclusion arrived within me was that as long as properties are not
modified, but only added and as long as it does not go against DT as an
ABI, it is ok.
I would like to hear from DT maintainers what the approach should be.
Regards
Afzal
[A] http://www.mail-archive.com/linux-omap@xxxxxxxxxxxxxxx/msg89408.html
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