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From: Pavel Machek <pavel@ucw.cz>
To: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: "Russell King - ARM Linux" <linux@arm.linux.org.uk>,
	"Tony Lindgren" <tony@atomide.com>,
	"Pali Rohár" <pali.rohar@gmail.com>,
	linux-omap <linux-omap@vger.kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Aaro Koskinen" <aaro.koskinen@iki.fi>,
	"Sebastian Reichel" <sre@kernel.org>,
	"Ivaylo Dimitrov" <ivo.g.dimitrov.75@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	"Laura Abbott" <lauraa@codeaurora.org>
Subject: Re: N900 v3.19-rc5 arm atags_to_fdt.c is broken
Date: Wed, 28 Jan 2015 00:17:11 +0100	[thread overview]
Message-ID: <20150127231711.GB27641@amd> (raw)
In-Reply-To: <alpine.LFD.2.11.1501271309450.1322@knanqh.ubzr>

On Tue 2015-01-27 13:50:22, Nicolas Pitre wrote:
> On Tue, 27 Jan 2015, Russell King - ARM Linux wrote:
> 
> > On Tue, Jan 27, 2015 at 10:16:24AM -0500, Nicolas Pitre wrote:
> > > On Tue, 27 Jan 2015, Pavel Machek wrote:
> > > > (Note, that in 3.19 dts for n900 got too big, so we are actually
> > > > triggering old bugs. That means that this is a regression fix, and
> > > > should go in ASAP).
> > > 
> > > It is queued here:
> > > http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=8294/1
> > 
> > Irrespective of that patch, I commented on another thread (about adding
> > the serial number to DT):
> > 
> > | How about something a little more radical.
> > | 
> > | Rather than trying to squeeze various ATAGs into DT, why don't we add a
> > | standard ATAG to contain the DT and pass that through into the kernel.
> > | This is IMHO how we _should_ have done the ATAG compatibility from the
> > | start.
> > | 
> > | That means we could get rid of most of the libfdt in the decompressor,
> > | and instead resolve the differences in the kernel.
> > 
> > That would allow us to get rid of all the FDT compatibility code in the
> > decompressor, and when we encounter these special ATAGs, we can deal with
> > them in the kernel instead of having to mess around with the DT.  I'd
> > also assume (although I haven't checked) that it would be much easier to
> > add additional DT properties in the kernel environment, rather than in
> > the rather restrictive decompressor environment.
> 
> Well...
> 
> I was initially against any ATAG-to-DT compatibility at all.  IMHO the 
> "right" solution is to update the bootloader.
> 
> However people complained that updating the bootloader wasn't possible. 
> I therefore suggested they go with a shim layer I termed the "impedance 
> matcher" acting like an intermediate boot stage converting their (often 
> unofficial and out-of-tree) ATAGs into proper DT nodes.  Some people did 
> exactly that and it works wonderfully for them. It also works 
> wonderfully for kernel maintenance as the platform specific tweaks are 
> kept out of the kernel tree.
> 
> Still, that wasn't good enough for some cases as the move to DT 
> regressed some platforms that just used to work before.  Concatenating a 
> DTB to zImage was tolerable but installing an additional shim layer was 
> too much.  Hence the ATAG-to-DT compat code in the decompressor.  This 
> was meant to smooth things around the transition to DT, etc.  After all, 
> those devices with non-replaceable bootloaders where shim layers are not 
> possible should get out of commission eventually?

N900 is still phone that is best-supported by the mainline,
AFAICT. Yes, it is rather sad, but it means that no, it is probably
not going out of commission anytime soon.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

  parent reply	other threads:[~2015-01-27 23:17 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-23 21:39 Pali Rohár
2015-01-23 22:36 ` Pali Rohár
2015-01-23 23:48   ` Pavel Machek
2015-01-24  9:04     ` Pali Rohár
2015-01-26 16:14   ` Tony Lindgren
2015-01-26 16:23     ` Pali Rohár
2015-01-26 17:03       ` Tony Lindgren
2015-01-26 18:57         ` Nicolas Pitre
2015-01-26 21:48           ` Pavel Machek
2015-01-27  0:06             ` Nicolas Pitre
2015-01-27 13:37           ` Pavel Machek
2015-01-27 15:16             ` Nicolas Pitre
2015-01-27 15:26               ` Pali Rohár
2015-01-27 15:26               ` Tony Lindgren
2015-01-27 17:53               ` Russell King - ARM Linux
2015-01-27 18:50                 ` Nicolas Pitre
2015-01-27 23:09                   ` Aaro Koskinen
2015-01-27 23:17                   ` Pavel Machek [this message]
2015-02-02 13:39               ` Pavel Machek
2015-02-02 13:56                 ` Nicolas Pitre

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