On 8/12/2011 5:02 AM, David Gibson wrote:
On Thu, Aug 11, 2011 at 02:28:55PM +0200, Cousson, Benoit wrote:
On 8/10/2011 9:22 PM, Grant Likely wrote:
On Tue, Aug 9, 2011 at 7:52 PM, David Gibson
<da...@gibson.dropbear.id.au> wrote:
On Tue, Aug 09, 2011 at 11:53:32PM +0200, Cousson, Benoit wrote:
On 8/9/2011 11:49 PM, Grant Likely wrote:
That won't work either because that also breaks the existing 'reg'
binding. Anything you do will need to supplement the existing
binding without changing it in an incompatible way.
OK, but can we add a new attribute then? reg2, reg_ng, reg_plusplus,
reg_named...?
He already suggested reg-names to be interpreted in parallel with the
existing reg property. The (serious) problem with replacing the reg
property is that it will break all existing OSes (including old Linux
versions) that don't understand the new property.
Of course, the problem with reg-names is that it will be ignored by
older OSes, and so 'reg' must still be in the correct order. In which
case you could argue it's more sensible to just have a static place to
name mapping in the Linux driver.
In short, yes, named reg elements in the DT would be nice in theory,
but I'm not convinced it's worth a DT flag day to accomplish it.
I'm inclined the same way, though I agree with the replies that point
out it wouldn't result in a 'flag day' because existing bindings
cannot become incompatible. The problem I have is that adding
reg-names or similar implies that ordering of the reg property is no
longer defined which I absolutely do not think is a good idea.
That will not be an issue if "reg-named" is a completely new node.
It will replace the "reg" node only when a named entry is needed.
Most devices will use the regular "reg" entry, and only the one that
need extra information will use the reg-named.
Um, you seem to be confusing nodes and properties here.
I don't think so. What I was proposing before was something like that:
dev {
reg_named {
name = "foo_wrapper";
start =<0x10000>;
end =<0x200>;
}
reg_named {
name = "foo";
start =<0x20000>;
end =<0x200>;
}
}
So, AFAIK, this is a node and not a property, isn't it?
OK, I was proposing as well something at attribute level:
reg_named = <0x10000 0x200>, "foo_wrapper", <0x20000 0x200>, "foo";
But I'm not sure it is easy to parse. Moreover, I cannot find a way to
differentiate a string from a cell in the property, so maybe I'm missing
something.
That seems to be pretty straightforward to implement, and as soon as
it is useful even for a couple of drivers, it worth adding it.
It is anyway better than having to add a custom property to get the
information we will miss otherwise.
Moreover, since some drivers are relying on that call, it will avoid
having to add extra code for nothing if CONFIG_OF is set.
It will allow the driver to use a pretty standard API in anycase vs
using platform_get_resource + some extra optional calls to of_
functions + some code to get the information for non-DT build.
You don't need to add stuff to the DT to use the byname interface.
Really. All you need is a way for the driver (well match table entry,
really) to provide a list of names to attach to the reg entries in
order.
That looks interesting, but I'm not sure to understand how it works.
Do you have an example?
It still looks like I will have to add some extra stuff in the driver,
whereas I will not have to if the DT core can handle that new reg_named.
Please, stick with the established convention and explicitly order
'reg' and 'interrupts' properties. If there is a specific use case
where this doesn't work, then bring it up, but I haven't seen any yet.
There will always be some alternatives, but they will be uglier, and
the effort to add some extra node to DT is so small, that it is
better to do that instead of adding some useless extra code in the
driver.
The current users of _byname that I've looked seem to only use it for
convenience, not because a register range may be optional. ie. they
all fail out if a reg resource isn't present.
If that API can help the driver writer and can avoid adding 10 lines
of code, it is still useful to use it.
To be honest, I still do not understand why you are so reluctant to
add that small feature.
Because this is a totally new basic feature to add to the DT
bindings. Once in there, we're stuck with it indefinitely, which
means it warrants considerably more conservatism than mere internal
code changes which can be easily updated or reverted.
OK, so it means that we need to be very careful with the design, but
does not mean it should be rejected.
Since that feature can be useful for some people, it still worth doing
it. Or do we have to keep that bindings for OMAP only?
In a period of consolidation, that does not seems to be the right solution.
Bottom-line, I can start with a RFC patch to add a new bindings and see
it is make sense to go further with it.
Benoit
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