linux-kernel - Re: [RFC PATCH v2 0/1] of: easier debugging for node life cycle issues

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Date:   Thu, 25 Jan 2018 13:49:01 -0800
From:   Frank Rowand <frowand.list@...il.com>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, devicetree@...r.kernel.org,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-renesas-soc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Rob Herring <robh+dt@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 0/1] of: easier debugging for node life cycle
 issues

Hi Wolfram,

On 01/25/18 03:03, Steven Rostedt wrote:
> On Wed, 24 Jan 2018 22:55:13 -0800
> Frank Rowand <frowand.list@...il.com> wrote:
> 
>> Hi Steve,
> 
>>
>> Off the top of your head, can you tell me know early in the boot
>> process a trace_event can be called and successfully provide the
>> data to someone trying to debug early boot issues?
> 
> The trace events are enabled by early_initcall().

< snip >

This means that ftrace can not be used for the of_node_get(),
of_node_put(), and of_node_release() debug info, because
these functions are called before early_initcall().  Please
use pr_debug() for these functions.

As far as I know, the of_reconfig_notify() could remain an
ftrace instrumented function.  But now that the only thing
that would be ftrace instrumented is of_reconfig_notify(),
I don't see a strong justification for changing the existing
pr_debug() calls to an ftrace alternative.  Though I suspect
the original author of the patch still might desire to have
the "#ifdef DEBUG" surrounding the pr_debug() calls removed
since one of his issues was having to recompile his kernel
to do his debugging.

-Frank