linux-kernel - Re: [PATCH 0/5] ARM: orion5x/dove/mv78xx0 multiplatform

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Date:	Fri, 11 Dec 2015 18:46:02 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Arnd Bergmann <arnd@...db.de>, Detlef Vollmann <dv@...lmann.ch>,
	linux-arm-kernel@...ts.infradead.org, Andrew Lunn <andrew@...n.ch>,
	Russell King <linux@....linux.org.uk>,
	Benjamin Cama <benoar@...ka.fr>, linux-kernel@...r.kernel.org,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	"Evgeniy A. Dushistov" <dushistov@...l.ru>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 0/5] ARM: orion5x/dove/mv78xx0 multiplatform

On Fri, Dec 11, 2015 at 10:27:30AM -0800, Josh Triplett wrote:
> On Fri, Dec 11, 2015 at 01:36:01PM +0000, Jason Cooper wrote:
> > +Josh
> > 
> > Hey Arnd, Detlef,
> > 
> > On Fri, Dec 11, 2015 at 12:10:55AM +0100, Arnd Bergmann wrote:
> > > On Thursday 10 December 2015 23:00:24 Detlef Vollmann wrote:
> > > > On 12/10/15 22:29, Arnd Bergmann wrote:
> > > > > On Thursday 10 December 2015 22:14:25 Detlef Vollmann wrote:
> > > > >> On 12/10/15 21:59, Arnd Bergmann wrote:
> > > > > It may also be worth investigating what has made CONFIG_OF so costly,
> > > > Probably because too much is done at runtime and too few things can
> > > > be fixed at build time.
> > > > 
> > > > > maybe we can reduce this a bit again.
> > > > Probably not without turning the wheel backward :-(
> > > > 
> > > > So for the test: yes it works, but I'm unhappy with it.
> > > 
> > > I'm not too happy about adding 80kb to the uncompressed kernel 
> > > image either. I've spent some more time now trying to find where
> > > we added the bloat. It's mainly in drivers, not in arch specific
> > > code, a kilobyte here and there eventually adds up, but the largest
> > > portion with a little over 50% of the total diff is drivers/of.
> > 
> > Wasn't there an idea kicked around a while ago to create a
> > dt2boardfile script/executable*?  Then, during kernel configuration, you
> > enable it and select which dts file you want.  It would disable
> > CONFIG_OF, multiplatform, etc.  And generate a board_file.c from the dts
> > file.
> > 
> > If anything, it might be worth asking the kernel tinification [1], [2]
> > folks if they'd be interested in taking this on...
> 
> No objection if you want to add it to the task list on
> tiny.wiki.kernel.org (on the more difficult end).

Done.

> I don't know if you could generate a board file, but I do wonder if you
> could effectively compile in a parsed description and ditch the parser.
> Bonus if you can make the values parsed out of it into compile-time
> constants for constant folding.

After a bit of discussion with Arnd on irc, I agree.  Going to  a board
file doesn't really work since the logic is now mostly in the drivers
probe functions.

The dts parsing -> compile-time constants is worth looking into.

thx,

Jason.
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