linux-kernel - Re: [PATCH] Open Firmware device tree virtual filesystem

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Date:	Wed, 3 Jan 2007 01:35:41 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	linux-kernel@...r.kernel.org, devel@...top.org,
	David Miller <davem@...emloft.net>, jengelh@...ux01.gwdg.de,
	Mitch Bradley <wmb@...mworks.com>, jg@...top.org
Subject: Re: [PATCH] Open Firmware device tree virtual filesystem

>> Leaving aside the issue of in-memory or not, I don't think
>> it is realistic to think any completely common implementation
>> will work for this -- it might for current SPARC+PowerPC+OLPC,
>> but more stuff will be added over time...
>
> And ? I don't see why a mostly common implementations wouldn't work,
> provided that we provide hooks in the right place.

Now read back and see that that is very close to what I said.

> It's pretty clear to me that the actual construction of the in-memory
> tree will remain platform specific (powerpc has this flattened format
> used for the trampoline for example and so far, I don't think other
> platforms plan to use it, though it might be a good idea too :-) sparc
> has "issues" related to firmwares that aren't quite OF, etc...)
>
> But it's also clear that the in-kernel representation, accessors and
> filesystem could/should be totally identical, including all we build on
> top, like prom_parse, of_device/of_platform device stuff etc.. (for
> which I need to re-sync with davem too btw, as he did some fixes that I
> didn't backport to powerpc... sigh)

The biggest problem is the huge collection of workarounds we have
for PowerPC alone already -- if that can be moved into some
quirk collection thing, where certain quirks are only run on some
systems, it might scale.

You'll also have to deal with endianness finally (you can *not*
access an integer property via an int*).

It will be easiest to start with a biggish collection of hooks,
that doesn't require too much code change, and slowly converge
stuff.

> The other -one- thing that has to be different is the write back for
> properties that can be changed (/options typically) where the write 
> back
> mecanism is definitely platform specific.

All properties can be changed, any new property can be created.
Oh you mean after you killed OF -- yeah, it gets a bit harder
then eh :-)


Segher

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