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

From	Arnd Bergmann <arnd@arndb.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry
Date	2015-11-28 13:30 +0100
Message-ID	<qzMNz-oi-11@gated-at.bofh.it> (permalink)
References	<pLLOj-5uN-37@gated-at.bofh.it> <qzyrf-82O-5@gated-at.bofh.it> <qzACK-Q6-7@gated-at.bofh.it>
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On Friday 27 November 2015 18:28:50 Nicolas Pitre wrote:
> On Fri, 27 Nov 2015, Arnd Bergmann wrote:
> 
> > I don't mind creating the /proc/atags compatibility hack from the kernel
> > for a DT based N700 kernel, as long as we limit it as much as we can
> > to the machines that need it. Leaving a board file for the N700 in place
> > that contains the procfs code (and not much more) seems reasonable
> > here, as we are talking about a board specific hack and the whole point
> > appears to be running unmodified user space.
> > 
> > Regarding how to get the data into the kernel in the first place, my
> > preferred choice would still be to have an intermediate bootloader
> > such as pxa-impedance-matcher, but I won't complain if others are
> > happy enough about putting it into the ATAGS compat code we already
> > have, as long as it's limited to the boards we know need it.
> 
> Assuming you have a N700 board file for special procfs code, then why 
> not getting at the atags in memory where the bootloader has put them 
> directly from that same board file? This way it'll really be limited to 
> the board we know needs it and the special exception will be contained 
> to that one file.  Amongst the machine specific hooks, there is one that 
> gets invoked early during boot before those atags are overwritten.

I didn't realize this was possible, as we don't know the atags pointer
when we instead get a DTB pointer. However you are right: the board
file knows exactly that the atag_offset is 0x100, so we can grab it
from there, and that will make the implementation really easy and
contained to a single file that has access to the atags and that
can create the /proc/atags file for it.

	Arnd
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Thread

Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Pavel Machek <pavel@ucw.cz> - 2015-11-22 08:00 +0100
  Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Pali Rohár <pali.rohar@gmail.com> - 2015-11-23 15:50 +0100
    Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Tony Lindgren <tony@atomide.com> - 2015-11-25 19:20 +0100
      Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Arnd Bergmann <arnd@arndb.de> - 2015-11-25 20:50 +0100
        Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Tony Lindgren <tony@atomide.com> - 2015-11-25 22:10 +0100
          Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Arnd Bergmann <arnd@arndb.de> - 2015-11-25 22:40 +0100
            Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Pali Rohár <pali.rohar@gmail.com> - 2015-11-25 22:50 +0100
              Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Arnd Bergmann <arnd@arndb.de> - 2015-11-25 23:00 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Pali Rohár <pali.rohar@gmail.com> - 2015-11-25 23:10 +0100
          Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags"  entry Frank Rowand <frowand.list@gmail.com> - 2015-11-26 05:30 +0100
            Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Pali Rohár <pali.rohar@gmail.com> - 2015-11-26 10:10 +0100
              Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Tony Lindgren <tony@atomide.com> - 2015-11-26 21:50 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> - 2015-11-26 22:20 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Pali Rohár <pali.rohar@gmail.com> - 2015-11-27 09:40 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Michael Trimarchi <michael@amarulasolutions.com> - 2015-11-27 09:50 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Michael Trimarchi <michael@amarulasolutions.com> - 2015-11-27 10:00 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Tony Lindgren <tony@atomide.com> - 2015-11-27 16:00 +0100
              Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-27 14:30 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-27 21:00 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Arnd Bergmann <arnd@arndb.de> - 2015-11-27 22:10 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-11-28 00:30 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Arnd Bergmann <arnd@arndb.de> - 2015-11-28 13:30 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-28 14:00 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-28 13:40 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-11-28 18:40 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags"  entry Frank Rowand <frowand.list@gmail.com> - 2015-11-28 22:10 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-29 19:20 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Pali Rohár <pali.rohar@gmail.com> - 2015-11-29 19:20 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-30 00:20 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry Pali Rohár <pali.rohar@gmail.com> - 2015-11-30 01:20 +0100
                Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT  "/chosen/linux,atags" entry Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-11-30 01:20 +0100

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