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

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Message-ID: <d81f2067-db9f-eeca-7d65-956d5f772093@daenzer.net>
Date:   Thu, 6 Dec 2018 10:21:40 +0100
From:   Michel Dänzer <michel@...nzer.net>
To:     Chris Wilson <chris@...is-wilson.co.uk>,
        "Zhang, Jerry(Junwei)" <Jerry.Zhang@....com>,
        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

On 2018-12-06 10:12 a.m., Chris Wilson wrote:
> 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.

We still #define DEBUG if CONFIG_DYNAMIC_DEBUG isn't defined, so it's
still 1b), not 1a).


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer