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

From: Frank Rowand <frowand.list@gmail.com>
To: Tony Lindgren <tony@atomide.com>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
	"Pali Rohár" <pali.rohar@gmail.com>,
	"Pavel Machek" <pavel@ucw.cz>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"Russell King - ARM Linux" <linux@arm.linux.org.uk>,
	"Laura Abbott" <lauraa@codeaurora.org>,
	"Grant Likely" <grant.likely@linaro.org>,
	"Rob Herring" <robherring2@gmail.com>,
	"Will Deacon" <will.deacon@arm.com>,
	"Ivaylo Dimitrov" <ivo.g.dimitrov.75@gmail.com>,
	"Sebastian Reichel" <sre@debian.org>,
	"Andreas Färber" <afaerber@suse.de>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org
Subject: Re: [PATCH 5/5] arm: boot: store ATAGs structure into DT "/chosen/linux,atags" entry
Date: Wed, 25 Nov 2015 20:19:21 -0800	[thread overview]
Message-ID: <56568849.5080103@gmail.com> (raw)
In-Reply-To: <20151125210310.GT2517@atomide.com>

On 11/25/2015 1:03 PM, Tony Lindgren wrote:
> * Arnd Bergmann <arnd@arndb.de> [151125 11:50]:
>> On Wednesday 25 November 2015 10:16:44 Tony Lindgren wrote:
>>> * Pali Rohár <pali.rohar@gmail.com> [151123 06:46]:
>>>> On Sunday 22 November 2015 07:51:46 Pavel Machek wrote:
>>>>> On Wed 2015-11-11 17:10:46, Frank Rowand wrote:
>>>>>> Adding devicetree list.
>>>>>>
>>>>>> Thread starts at
>>>>>> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/354459.html
>>>>>>
>>>>>> On 11/5/2015 8:17 AM, Tony Lindgren wrote:
>>>>>>> * Pali Rohár <pali.rohar@gmail.com> [151105 03:41]:
>>>>>>>> On Tuesday 13 October 2015 16:37:46 Pali Rohár wrote:
>>>>>>>>> On Monday 12 October 2015 13:45:09 Tony Lindgren wrote:
>>>>>>>>>> * Pali Rohár <pali.rohar@gmail.com> [151012 13:29]:
>>>>>>>>>>> On Monday 12 October 2015 22:16:40 Tony Lindgren wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> Pali, any news on posting an updated series with the comments
>>>>>>>>>>>> addressed in this thread? It seems that we all pretty much agree
>>>>>>>>>>>> what needs to be done.
>>>>>>
>>>>>> I'm not real happy with the concept of patches 4 and 5 in this series.
>>>>>> My concern is that those two patches are using the FDT as a transport
>>>>>> mechanism for a binary blob (the atags object).
>>>>>
>>>>> Umm. Ok. Do you have alternative proposal that works for everyone?
>>>>>
>>>>> I mean. This discussion was going for quite a long time, and it would
>>>>> be nice to have some solution... patch proposal... something.
>>>>>                                                                     Pavel
>>>>
>>>> Yes, discussion is going for a long time! So should I spend time for
>>>> adding documentation to my solution (this is last one thing which is
>>>> missing)? Or my solution is wrong and somebody else will propose new?
>>>> I do not want to spend time on something which will be rejected and
>>>> discarded.
>>>
>>> At least I don't have better solutions in mind.
>>
>> I would be happier if we could restrict this as much as possible to the
>> boards that need it, as an opt-in. That way it doesn't become an ABI

The feature (in whatever form it takes) should be definitely be highly
restricted and marked as deprecated.

>> for people that don't already rely in this information. How about
>> adding a check the code adds the linux,atags property to do it
>> only for a whitelist of board numbers?
> 
> Or populate /proc/atags only for the ones that need it from machine
> specific init_early?

This is circling back to the first comment from Russell King where
he suggested a legacy file for the N900 which calls save_atags():

    Are the ATAGs at a fixed address on the N900?  Can that be handled in
    some kind of legacy file for the N900 which calls save_atags() on it, so
    we don't end up introducing yet more stuff that we have to maintain into
    the distant future?  If not, what about copying a known working atag
    structure into a legacy file for the N900?

It seems to me that patches 1, 2, 4, and 5 could be replaced by this
approach.

Regards,

Frank