linux-kernel - Re: [PATCH] arm: dt: Initialize boot_command_line from CONFIG_CMDLINE in case DT does not provide /chosen/bootargs

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Date:   Fri, 16 Dec 2016 12:46:12 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Tony Lindgren <tony@...mide.com>,
        Javier Martinez Canillas <javier@....samsung.com>
Cc:     "Russell King - ARM Linux" <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Robin Murphy <robin.murphy@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ben Dooks <ben-linux@...ff.org>,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        Sebastian Reichel <sre@...nel.org>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Pavel Machek <pavel@....cz>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm: dt: Initialize boot_command_line from CONFIG_CMDLINE in case DT does not provide /chosen/bootargs

On Thursday 15 December 2016 01:09:20 Pali Rohár wrote:
> On Thursday 15 December 2016 00:52:24 Russell King - ARM Linux wrote:
> > On Wed, Dec 14, 2016 at 10:12:43PM +0100, Pali Rohár wrote:
> > > Commit 008a2ebcd677 ("ARM: dts: omap3: Remove skeleton.dtsi
> > > usage") broke support for setting cmdline on Nokia N900 via
> > > CONFIG_CMDLINE.
> > > 
> > > It is because arm code booted in DT mode parse cmdline only via
> > > function early_init_dt_scan_chosen() and that function does not
> > > fill variable boot_command_line when DTB does not contain /chosen
> > > entry. It is called from function early_init_dt_scan_nodes() in
> > > setup_machine_fdt().
> > > 
> > > This patch fixes it by explicitly filling boot_command_line in
> > > function setup_machine_fdt() after calling
> > > early_init_dt_scan_nodes() in case boot_command_line still
> > > remains empty.
> > 
> > This looks like a hack.
> > 
> > First, the matter of the ATAGs compatibility.  The decompressor
> > relies on there being a pre-existing /chosen node to insert the
> > command line and other parameters into.  If we've dropped it (by
> > dropping skeleton.dtsi) then we've just regressed more than just
> > N900 - the decompressor won't be able to merge the ATAGs into the
> > concatenated FDT.
> 
> Hm... I did not think about it. But right this can be broken too...

Tony, Javier: are you aware of above ↑↑↑ problem?

It looks like commit 008a2ebcd677 ("ARM: dts: omap3: Remove 
skeleton.dtsi usage") should be really reverted.

-- 
Pali Rohár
pali.rohar@...il.com

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