Date: Fri, 27 Nov 2015 18:28:50 -0500 (EST)
From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Arnd Bergmann <arnd@arndb.de>
cc: linux-arm-kernel@lists.infradead.org,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        =?ISO-8859-15?Q?Pali_Roh=E1r?= <pali.rohar@gmail.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>,
        Laura Abbott <lauraa@codeaurora.org>, Tony Lindgren <tony@atomide.com>,
        Sebastian Reichel <sre@debian.org>, Will Deacon <will.deacon@arm.com>,
        linux-kernel@vger.kernel.org, Rob Herring <robherring2@gmail.com>,
        Pavel Machek <pavel@ucw.cz>, Grant Likely <grant.likely@linaro.org>,
        linux-omap@vger.kernel.org, Frank Rowand <frowand.list@gmail.com>,
        =?ISO-8859-15?Q?Andreas_F=E4rber?= <afaerber@suse.de>
Subject: Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT
 "/chosen/linux,atags" entry
In-Reply-To: <11537945.4HX4Y84tjV@wuerfel>
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References: <20150713131902.GH26485@atomide.com> <20151127132722.GA30871@n2100.arm.linux.org.uk> <20151127195148.GB30871@n2100.arm.linux.org.uk> <11537945.4HX4Y84tjV@wuerfel>
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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.


Nicolas
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