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

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Date:   Thu, 06 Dec 2018 09:12:59 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     "Zhang, Jerry\(Junwei\)" <Jerry.Zhang@....com>,
        Michel Dänzer <michel@...nzer.net>,
        Christian Koenig <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>, Huang Rui <ray.huang@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>
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

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@....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@....com>
> Reviewed-by: Junwei Zhang <Jerry.Zhang@....com>

At the cost of 1a? Nah.
-Chris