linux-kernel - Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry

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Date:	Fri, 27 Nov 2015 09:38:33 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Frank Rowand <frowand.list@...il.com>,
	Arnd Bergmann <arnd@...db.de>, Pavel Machek <pavel@....cz>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Laura Abbott <lauraa@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robherring2@...il.com>,
	Will Deacon <will.deacon@....com>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Sebastian Reichel <sre@...ian.org>,
	Andreas Färber <afaerber@...e.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org
Subject: Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT
 "/chosen/linux,atags" entry

On Thursday 26 November 2015 12:39:30 Tony Lindgren wrote:
> Just to explore options.. How about make a minimal device driver that
> just loads the atags blob from /lib/firmware and then shows it in
> /proc/atags? Of course some checking on the atags should be done by
> the driver..

And who can dynamically create that blob file in /lib/firmware? If
kernel does not export those atags (somehow) from bootloader, then
userspace is not able to create that blob... cyclic problem.

So no, problem is that bootloader provides via custom atags dynamic
information like: boot reason (how was device started, by rtc alarm? by
reboot? by usb charger? by power button?), boot mode (should be enter
into firmware update mode?, is this normal boot mode?), ... and those
information are needed for some proprietary software (e.g. firmware
upgrade/flash) but also by any other open source applications (based on
usb charger we enter different runlevel -- for just only charging
device).

-- 
Pali Rohár
pali.rohar@...il.com
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