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To:     "Zhang, Jerry\(Junwei\)" <Jerry.Zhang@amd.com>,
        =?utf-8?q?Michel_D=C3=A4nzer?= <michel@daenzer.net>,
        Christian Koenig <christian.koenig@amd.com>,
        David Airlie <airlied@linux.ie>, Huang Rui <ray.huang@amd.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Sean Paul <sean@poorly.run>
From:   Chris Wilson <chris@chris-wilson.co.uk>
In-Reply-To: <10fca21a-5d7c-fe9e-07f0-6200e9de538e@amd.com>
Cc:     linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
References: <20181205165621.5805-1-michel@daenzer.net>
 <10fca21a-5d7c-fe9e-07f0-6200e9de538e@amd.com>
Message-ID: <154408757908.3572.9138595858555797029@skylake-alporthouse-com>
User-Agent: alot/0.6
Subject: Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC_DEBUG is disabled
Date:   Thu, 06 Dec 2018 09:12:59 +0000
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Quoting Zhang, Jerry(Junwei) (2018-12-06 02:40:42)
> On 12/6/18 12:56 AM, Michel Dänzer wrote:
> > From: Michel Dänzer <michel.daenzer@amd.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")
> > Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
> Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>

At the cost of 1a? Nah.
-Chris