Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC_DEBUG is disabled

From: "Michel Dänzer" <michel@daenzer.net>
To: Joe Perches <joe@perches.com>,
	"Zhang, Jerry(Junwei)" <Jerry.Zhang@amd.com>,
	Christian Koenig <christian.koenig@amd.com>,
	Huang Rui <ray.huang@amd.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
	Chris Wilson <chris@chris-wilson.co.uk>
Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC_DEBUG is disabled
Date: Thu, 6 Dec 2018 10:23:18 +0100	[thread overview]
Message-ID: <276fbf7f-d33f-83a5-cb88-bd4051dc03ba@daenzer.net> (raw)
In-Reply-To: <1586a49594d30b4bf4d88eba0d258e21efd26da2.camel@perches.com>

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@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")
> 
> 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.

> And why didn't you cc Chris Wilson, the author of that patch?

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.

>>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
>> Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
>>
>>> ---
>>>   drivers/gpu/drm/drm_print.c | 6 ++++--
>>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
>>> index 0e7fc3e7dfb4..ee56e4a1b343 100644
>>> --- a/drivers/gpu/drm/drm_print.c
>>> +++ b/drivers/gpu/drm/drm_print.c
>>> @@ -23,11 +23,13 @@
>>>    * Rob Clark <robdclark@gmail.com>
>>>    */
>>>   
>>> -#define DEBUG /* for pr_debug() */
>>> -
>>>   #include <stdarg.h>
>>>   #include <linux/seq_file.h>
>>>   #include <drm/drmP.h>
>>> +
>>> +#ifndef CONFIG_DYNAMIC_DEBUG
>>> +#define DEBUG /* for pr_debug() */
>>> +#endif
>>>   #include <drm/drm_print.h>
>>>   
>>>   void __drm_puts_coredump(struct drm_printer *p, const char *str)
> 
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> 

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