linux-kernel - Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC

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Message-ID: <e7859ce4b8417b094604d9ab4740d338730e38bf.camel@perches.com>
Date:   Thu, 06 Dec 2018 03:41:51 -0800
From:   Joe Perches <joe@...ches.com>
To:     Michel Dänzer <michel@...nzer.net>,
        "Zhang, Jerry(Junwei)" <Jerry.Zhang@....com>,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Chris Wilson <chris@...is-wilson.co.uk>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC_DEBUG is
 disabled

On Thu, 2018-12-06 at 10:23 +0100, Michel Dänzer wrote:
> On 2018-12-06 3:51 a.m., Joe Perches wrote:
> > On Thu, 2018-12-06 at 10:40 +0800, Zhang, Jerry(Junwei) wrote:
> > > On 12/6/18 12:56 AM, Michel Dänzer wrote:
> > > > From: Michel Dänzer <michel.daenzer@....com>
> > > > 
> > > > The following cases are possible for pr_debug():
> > > > 
> > > > 1. CONFIG_DYNAMIC_DEBUG disabled
> > > >     a) DEBUG not defined: pr_debug() translates to no_printk(...), i.e.
> > > >        it never generates any output.
> > > >     b) DEBUG defined: pr_debug() translates to printk(KERN_DEBUG ...),
> > > >        i.e. it generates output which doesn't appear in dmesg by default,
> > > >        can be enabled dynamically.
> > > > 
> > > > 2. CONFIG_DYNAMIC_DEBUG enabled: pr_debug() translates to
> > > >     dynamic_pr_debug()
> > > >     a) DEBUG not defined: dynamic_pr_debug() generates no output by
> > > >        default, can be enabled dynamically.
> > > >     b) DEBUG defined: dynamic_pr_debug() generates output by default,
> > > >        can be disabled dynamically.
> > > > 
> > > > The intention for drm_debug_printer() is to generate output which
> > > > doesn't appear in dmesg by default, but can be enabled dynamically, i.e.
> > > > cases 1b) and 2a). However, defining DEBUG unconditionally gave us 2b)
> > > > instead of 2a) with CONFIG_DYNAMIC_DEBUG enabled.
> > > > 
> > > > Fixes: 79a5ad2fdb3c ("drm: Enable pr_debug() for drm_printer")
> > 
> > I very much doubt this is a fix.
> > 
> > Did you read the commit log for this commit?
> > 
> > It says "make sure it will always produce output"
> 
> I thought the commit log covered this, suggestions for improvement welcome.
> 
> Chris' change addressed case 1a), but also took us from 2a) to 2b). But
> we want 2a)

> I suspect Chris missed that pr_debug()'s output is visible by default if
> CONFIG_DYNAMIC_DEBUG and DEBUG are both defined.

I believe you and Chris have different goals and that your
point of 2b is
misguided.

I think the language used in the Chris' commit log is
plain ans obvious.  'always produce output'.

> > And why didn't you cc Chris Wilson, the author of that patch?k
> 
> I used the get_maintainer.pl script. Thanks for adding Chris.
> P.S. FYI, your e-mail had a very aggressive tone to me, not sure what for.

No worries.

I think the language I used is also plain and obvious
and you are overreading.

cheers, Joe