From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <frowand.list@gmail.com>
Received: from mail-pg0-x241.google.com (mail-pg0-x241.google.com
 [IPv6:2607:f8b0:400e:c05::241])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (No client certificate requested)
 by lists.ozlabs.org (Postfix) with ESMTPS id 3zSFzk3lG2zDqlB
 for <linuxppc-dev@lists.ozlabs.org>; Fri, 26 Jan 2018 08:49:06 +1100 (AEDT)
Received: by mail-pg0-x241.google.com with SMTP id s9so5910691pgq.13
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 25 Jan 2018 13:49:06 -0800 (PST)
Subject: Re: [RFC PATCH v2 0/1] of: easier debugging for node life cycle issues
To: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, devicetree@vger.kernel.org,
 Tyrel Datwyler <tyreld@linux.vnet.ibm.com>,
 Geert Uytterhoeven <geert@linux-m68k.org>,
 linux-renesas-soc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
 Rob Herring <robh+dt@kernel.org>, linux-kernel@vger.kernel.org
References: <20180121143117.19805-1-wsa+renesas@sang-engineering.com>
 <00fc90ee-de26-f819-9c81-27d06918564d@gmail.com>
 <20180125060330.781667e9@vmware.local.home>
From: Frank Rowand <frowand.list@gmail.com>
Message-ID: <a30d4cd3-0068-8cca-cc2f-ca207d0d278b@gmail.com>
Date: Thu, 25 Jan 2018 13:49:01 -0800
MIME-Version: 1.0
In-Reply-To: <20180125060330.781667e9@vmware.local.home>
Content-Type: text/plain; charset=utf-8
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

Hi Wolfram,

On 01/25/18 03:03, Steven Rostedt wrote:
> On Wed, 24 Jan 2018 22:55:13 -0800
> Frank Rowand <frowand.list@gmail.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