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

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Date:   Thu, 6 Dec 2018 17:14:04 +0100
From:   Michel Dänzer <michel@...nzer.net>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        "Zhang, Jerry(Junwei)" <Jerry.Zhang@....com>,
        Huang Rui <ray.huang@....com>, Joe Perches <joe@...ches.com>,
        Sean Paul <sean@...rly.run>,
        Christian Koenig <christian.koenig@....com>
Subject: Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC_DEBUG is
 disabled

On 2018-12-06 5:10 p.m., Daniel Thompson wrote:
> On Thu, Dec 06, 2018 at 03:41:16PM +0100, Michel Dänzer wrote:
>> On 2018-12-06 1:23 p.m., Joe Perches wrote:
>>> On Thu, 2018-12-06 at 12:52 +0100, Michel Dänzer wrote:
>>>> In contrast to the 2b case, the pr_debug output isn't visible by default
>>>> with 1b, so the latter doesn't fit "always produce output" either.
>>>
>>> I think you are mistaken here.
>>
>> Still puzzled as to what you're hoping to achieve with that kind of
>> language. None of the confusion about this patch has been on my part. :)
>>
>>
>>> Adding #define DEBUG as Chris did enables pr_debug output
>>> and is your 1b.
>>>
>>> Perhaps your default console logging level is set to a
>>> non-default value.
>>
>> I have CONFIG_DYNAMIC_DEBUG enabled in my kernels. The problem addressed
>> by this patch is that messages from drm_debug_printer are visible by
>> default (case 2b), whereas they shouldn't be (case 2a, like 1b).
> 
> When enabled (either dynamically or statically) pr_debug() will emit
> output at KERN_DEBUG level regardless of whether CONFIG_DYNAMIC_DEBUG
> is defined or not.
> 
> Thus unless you change additional settings (either dynamically or
> statically) then debug messages should not be shown on the console
> because the default settings filter KERN_DEBUG messages. However they
> are available via dmesg and system loggers (syslogd, journal, etc).
> 
> The patch proposed will change the behaviour of the debug messages
> w.r.t. system loggers based on whether the user has enabled
> CONFIG_DYNAMIC_DEBUG or not, violating the principle of least surprise.

Ah, that makes sense now, thanks.

I'm withdrawing this patch.


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