[PATCH] ARM: Include Makefile.boot only when it exists
Russell King - ARM Linux
linux at arm.linux.org.uk
Fri Apr 29 09:33:40 EDT 2011
On Fri, Apr 29, 2011 at 08:32:59AM -0400, Nicolas Pitre wrote:
> On Fri, 29 Apr 2011, Russell King - ARM Linux wrote:
> > On Thu, Apr 28, 2011 at 09:00:08PM -0400, Nicolas Pitre wrote:
> > > On Thu, 28 Apr 2011, Russell King - ARM Linux wrote:
> > >
> > > > If/when we move to DT, do people think that Linus is going to accept
> > > > having the DT files in the kernel for all these platforms, and will he
> > > > be happy to see stuff like the files containing the OMAP clock definitions
> > > > being constantly patched? Remember, it's *exactly* this data which Linus
> > > > wants out of the kernel source.
> > >
> > > Well, here's what he said:
> > >
> > > |But trust me, if you start doing a better job at platform code, I
> > > |won't be complaining when I get lots of deleted code, or when I start
> > > |getting devicetree descriptions instead of new drivers.
> > > (http://article.gmane.org/gmane.linux.kernel/1121387)
> > >
> > > So of course this "getting devicetree descriptions" might be interpreted
> > > to mean different things.
> > >
> > > OTOH, the device tree source files can be arranged with common
> > > definitions in something like a header file that is included by board
> > > specific files. So, at least in theory, differences between similar
> > > boards should be small, hopefully smaller than the equivalent in C.
> > >
> > > Also, DT files should be a representation of the hardware which is meant
> > > to be stable. If it wasn't stable, there would be no point using a data
> > > structure that can also be used outside of the kernel. Remember that
> > > one of the selling point for DT is to be able to boot an existing kernel
> > > binary on yet-to-be-created hardware simply by creating the appropriate
> > > DT description for it. Hence the DT files for existing hardware
> > > shouldn't have to change even if the kernel side implementation does.
> > >
> > > > I suspect the answer to that is no. So I think we should start right now
> > > > with the idea that putting DT files - even the core SoC ones - into the
> > > > kernel isn't going to be acceptable.
> > >
> > > Well, if you look at arch/powerpc/boot/dts/* you'll find a bunch of
> > > board specific DT files in there already, and Linus has identified PPC
> > > as one architecture that did it right in his mind.
> > Sigh, you really don't understand.
> > For OMAP we're likely to see several dts files around 200K in size
> > describing _just_ the clock trees. As we've seen, the OMAP clock tree
> > information is modified fairly regularly, adding new clocks, changing
> > flags, and so forth.
> What do I not understand? Let me repeat myself again:
> | DT files should be a representation of the hardware which is meant to
> | be stable. [...] Hence the DT files for existing hardware shouldn't
> | have to change even if the kernel side implementation does.
> So there shouldn't be constant changes to those files as they are
> supposed to be hardware description only.
You really haven't seen what goes on in the OMAP community then. If
you think its possible to come up with a hardware description of the
OMAP clock tree which is right first time, you're in cloud cuckoo land.
Even the OMAP4 clock data which is supposedly generated from TIs
internal hardware database changes on a fairly regular basis. You'll
find that the per-clk flags get changed, the operations get changed,
It doesn't _matter_ how it is represented, it will continue to be patched
whether it's structures in a .c file (as it currently is) or whether it's
a device tree description for each clock.
So please, get rid of this stupid idea that its possible to come up with
a One True Hardware Description which is fixed for all time.
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