linux-kernel - Re: [PATCH v6] pstore/ram: Add ramoops support for the Flattened Device Tree.

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Message-ID: <51634826.5010602@gmail.com>
Date:	Mon, 08 Apr 2013 17:43:50 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Bryan Freed <bfreed@...omium.org>
CC:	Anton Vorontsov <anton@...msg.org>,
	Tony Luck <tony.luck@...el.com>,
	Kees Cook <keescook@...omium.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	Colin Cross <ccross@...roid.com>,
	Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v6] pstore/ram: Add ramoops support for the Flattened
 Device Tree.

On 04/08/2013 02:54 PM, Bryan Freed wrote:
> Sorry for dropping the ball on this one, Anton.
> 
> Thank you for your feedback and modifications in the code.
> I gotta ask, however, why do you completely remove key ramoops fields
> like record_size and ftrace_size?
> 
> From your 9/7/2012 comments (again, sorry for the delay in getting back to you):
>> Personally, I don't see how this fits into device tree. It doesn't
>> describe hardware, instead it's more a configuration stuff, which
>> usually we try to not put into the device tree.
>>
>> It would be better to have a sane defaults in ramoops, instead of
>> introducing more "virtual" stuff in the device tree. That is, feel
>> free to change defaults if they seem to be not enough for most your
>> setups.
> 
> So there are only two alternatives I can see to set these fields.
> 1. Pass kernel command line parameters, or
> 2. Modify the defaults in ram.c.
> 
> Neither of these alternatives is particularly clean to me.  The first
> is shunned to avoid clutter on the command line.
> And the second requires us to maintain our own version of ram.c or
> push our defaults on the rest of the community.
> 
> We (ok, maybe just 'I') prefer to keep our device specific values in
> the device tree, even though it is not strictly defining hardware in
> the system.
> What do you think of at least keeping the record_size, console_size
> and ftrace_size fields as optional in the ramoops device tree
> specification?
> 
> And as a more general question, why should we try not to put
> configuration in the device tree?  It seems like a great (and
> portable) place to put this stuff.
> It certainly seems better to have it there than hardwired in the
> kernel or tacked onto the kernel command line.

You have to account for the fact that you may not be able to update the
dtb which may be part of firmware. I can imagine you might want to
change some of the sizes frequently based on what you are doing and
trying to capture. So even if you put in the DT, you need some easy way
to override the settings. This could always be fixed-up by the
bootloader which is what is done for things we don't expect the firmware
to know like initrd address/size and kernel command line. This is why
the prior discussion I mentioned below suggested putting all this in the
/chosen node.

Rob

> 
> Thanks,
> 
> bryan.
> 
> On Sun, Apr 7, 2013 at 10:43 AM, Anton Vorontsov <anton@...msg.org> wrote:
>> On Thu, Apr 04, 2013 at 09:03:47PM -0500, Rob Herring wrote:
>>> On Mon, Sep 17, 2012 at 1:23 AM, Anton Vorontsov <cbouatmailru@...il.com> wrote:
>>>> On Fri, Sep 07, 2012 at 10:29:10PM -0700, Anton Vorontsov wrote:
>>>>> On Fri, Sep 07, 2012 at 11:29:36AM -0700, Bryan Freed wrote:
>>>>>> When called with a non-zero of_node, fill out a new ramoops_platform_data
>>>>>> with data from the specified Flattened Device Tree node.
>>>>>> Update ramoops documentation with the new FDT interface.
>>>>>> Update devicetree/binding documentation with pstore/ramoops.txt.
>>>>>
>>>>> Thanks for your work, Bryan! There were a few issues, I fixed
>>>>> them myself but I need your confirmation if you're OK w/ all
>>>>> the changes.
>>>> [...]
>>>>> So, the resulting patch is down below. But I have not pushed
>>>>> it out yet, I'm waiting for your sign off. If you're OK with the
>>>>> changes, please reply with
>>>>> 'Signed-off-by: Bryan Freed <bfreed@...omium.org>'
>>>>
>>>> Bryan, have you had a chance to look into this?
>>>
>>> Whatever happened to this? Olof was also looking at doing a binding
>>> back in Jan 2012:
>>>
>>> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg09905.html
>>
>> I don't know. Bryan's patch looked good, I'd happily apply it. But I still
>> need Bryan's Signed-off-by tag. :-/ Or, somebody needs to sign off on his
>> behalf (anyone from Chromium project?). Or redo the patch.
>>
>> Thanks,
>>
>> Anton

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