linux-kernel - Re: [PATCH v2 10/17] drm/vram-helper: make drm_vram_mm_debugfs

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Date:   Thu, 19 Mar 2020 15:27:29 +0300 (EAT)
From:   Wambui Karuga <wambui.karugax@...il.com>
To:     Daniel Vetter <daniel@...ll.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
        Wambui Karuga <wambui.karugax@...il.com>,
        Dave Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/17] drm/vram-helper: make drm_vram_mm_debugfs_init()
 return 0



On Thu, 19 Mar 2020, Daniel Vetter wrote:

> On Thu, Mar 19, 2020 at 08:55:24AM +0100, Greg KH wrote:
>> On Wed, Mar 18, 2020 at 08:10:43PM +0100, Daniel Vetter wrote:
>>> On Wed, Mar 18, 2020 at 5:58 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>>>>
>>>> On Wed, Mar 18, 2020 at 05:31:47PM +0100, Daniel Vetter wrote:
>>>>> On Wed, Mar 18, 2020 at 5:03 PM Wambui Karuga <wambui.karugax@...il.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, 18 Mar 2020, Daniel Vetter wrote:
>>>>>>
>>>>>>> On Tue, Mar 10, 2020 at 04:31:14PM +0300, Wambui Karuga wrote:
>>>>>>>> Since 987d65d01356 (drm: debugfs: make
>>>>>>>> drm_debugfs_create_files() never fail), drm_debugfs_create_files() never
>>>>>>>> fails and should return void. Therefore, remove its use as the
>>>>>>>> return value of drm_vram_mm_debugfs_init(), and have the function
>>>>>>>> return 0 directly.
>>>>>>>>
>>>>>>>> v2: have drm_vram_mm_debugfs_init() return 0 instead of void to avoid
>>>>>>>> introducing build issues and build breakage.
>>>>>>>>
>>>>>>>> References: https://lists.freedesktop.org/archives/dri-devel/2020-February/257183.html
>>>>>>>> Signed-off-by: Wambui Karuga <wambui.karugax@...il.com>
>>>>>>>> Acked-by: Thomas Zimmermann <tzimmermann@...e.de>
>>>>>>>> ---
>>>>>>>>  drivers/gpu/drm/drm_gem_vram_helper.c | 10 ++++------
>>>>>>>>  1 file changed, 4 insertions(+), 6 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
>>>>>>>> index 92a11bb42365..c8bcc8609650 100644
>>>>>>>> --- a/drivers/gpu/drm/drm_gem_vram_helper.c
>>>>>>>> +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
>>>>>>>> @@ -1048,14 +1048,12 @@ static const struct drm_info_list drm_vram_mm_debugfs_list[] = {
>>>>>>>>   */
>>>>>>>>  int drm_vram_mm_debugfs_init(struct drm_minor *minor)
>>>>>>>>  {
>>>>>>>> -    int ret = 0;
>>>>>>>> -
>>>>>>>>  #if defined(CONFIG_DEBUG_FS)
>>>>>>>
>>>>>>> Just noticed that this #if here is not needed, we already have a dummy
>>>>>>> function for that case. Care to write a quick patch to remove it? On top
>>>>>>> of this patch series here ofc, I'm in the processing of merging the entire
>>>>>>> pile.
>>>>>>>
>>>>>>> Thanks, Daniel
>>>>>> Hi Daniel,
>>>>>> Without this check here, and compiling without CONFIG_DEBUG_FS, this
>>>>>> function is run and the drm_debugfs_create_files() does not have access to
>>>>>> the parameters also protected by an #if above this function. So the change
>>>>>> throws an error for me. Is that correct?
>>>>>
>>>>> Hm right. Other drivers don't #ifdef out their debugfs file functions
>>>>> ... kinda a bit disappointing that we can't do this in the neatest way
>>>>> possible.
>>>>>
>>>>> Greg, has anyone ever suggested to convert the debugfs_create_file
>>>>> function (and similar things) to macros that don't use any of the
>>>>> arguments, and then also annotating all the static functions/tables as
>>>>> __maybe_unused and let the compiler garbage collect everything?
>>>>> Instead of explicit #ifdef in all the drivers ...
>>>>
>>>> No, no one has suggested that, having the functions be static inline
>>>> should make it all "just work" properly if debugfs is not enabled.  The
>>>> variables will not be used, so the compiler should just optimize them
>>>> away properly.
>>>>
>>>> No checks for CONFIG_DEBUG_FS should be needed anywhere in .c code.
>>>
>>> So the trouble with this one is that the static inline functions for
>>> the debugfs file are wrapped in a #if too, and hence if we drop the
>>> #if around the function call stuff won't compile. Should we drop all
>>> the #if in the .c file and assume the compiler will remove all the
>>> dead code and dead functions?
>>
>> Yes you should :)
>>
>> there should not be any need for #if in a .c file for debugfs stuff.
>
> Wambui, can you pls try that out? I.e. removing all the #if for
> CONFIG_DEBUG_FS from that file.

Removing them works with CONFIG_DEBUG_FS enabled or disabled.
I can send a patch for that.

wambui karuga
> -Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
>