linux-kernel - Re: [Nouveau] [PATCH] drm/nouveau: fix LEDS

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Message-ID: <CACvgo53jeezHQT6QJqfvV1KMW2v4r6z+n5Fg30kneEzBcFs7Fg@mail.gmail.com>
Date:   Tue, 8 Nov 2016 16:35:36 +0000
From:   Emil Velikov <emil.l.velikov@...il.com>
To:     Karol Herbst <karolherbst@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Nouveau] [PATCH] drm/nouveau: fix LEDS_CLASS=m configuration

On 8 November 2016 at 16:21, Karol Herbst <karolherbst@...il.com> wrote:
> 2016-11-08 17:12 GMT+01:00 Arnd Bergmann <arnd@...db.de>:
>> On Tuesday, November 8, 2016 5:07:01 PM CET Lukas Wunner wrote:
>>> On Tue, Nov 08, 2016 at 04:52:49PM +0100, Arnd Bergmann wrote:
>>> > The underlying problem is that we already have a number of other
>>> > symbols that either have "depends on LEDS_CLASS" or
>>> > "select LEDS_CLASS". To clean that up properly, we should either
>>> > make the symbol itself hidden and only select it from other drivers,
>>> > or use "depends on LEDS_CLASS" everywhere.
>>> >
>>> > Another option is to use the IS_REACHABLE() macro instead of IS_ENABLED()
>>> > in the header file, to stub out the calls into the new file, but
>>> > that can be a bit confusing.
>>>
>>> Why don't you just add empty inline stubs for nouveau_led_init / _fini /
>>> _suspend / _resume?
>>>
>>
>> That's what I was suggesting:
>>
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_led.h b/drivers/gpu/drm/nouveau/nouveau_led.h
>> index 9c9bb6ac938e..bc5f47cb516b 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_led.h
>> +++ b/drivers/gpu/drm/nouveau/nouveau_led.h
>> @@ -35,21 +35,21 @@ struct nouveau_led {
>>         struct led_classdev led;
>>  };
>>
>>  static inline struct nouveau_led *
>>  nouveau_led(struct drm_device *dev)
>>  {
>>         return nouveau_drm(dev)->led;
>>  }
>>
>>  /* nouveau_led.c */
>> -#if IS_ENABLED(CONFIG_LEDS_CLASS)
>> +#if IS_REACHABLE(CONFIG_LEDS_CLASS)
>>  int  nouveau_led_init(struct drm_device *dev);
>>  void nouveau_led_suspend(struct drm_device *dev);
>>  void nouveau_led_resume(struct drm_device *dev);
>>  void nouveau_led_fini(struct drm_device *dev);
>>  #else
>>  static inline int  nouveau_led_init(struct drm_device *dev) { return 0; };
>>  static inline void nouveau_led_suspend(struct drm_device *dev) { };
>>  static inline void nouveau_led_resume(struct drm_device *dev) { };
>>  static inline void nouveau_led_fini(struct drm_device *dev) { };
>>  #endif
>>
>> The downside is that now the nouveau_led_init() just won't be called
>> if CONFIG_LEDS_CLASS=m and CONFIG_DRM_NOUVEAU=y, which can be
>> surprising to users.
>
> yeah, it will. I guess it is fine to force LEDS to y if nouveau is set
> to y. The thinks I absolutely dislike is:
> 1. auto hiding of features I _want_ to have, because I would have to
> enable the dependencies first, which is like super annoying if there
> are somewhere else
> 2. preventing me from enabling something, cause the dependency is missing.
>
> We should clarify first if we actually want to enable those features
> optionally, because there isn't much of a reason not to enable the
> dependencies, except embedded systems. We have a lot more stuff where
> we could add things like that: hwmon, debugfs, acpi, compat and maybe
> there are even more things
>
Sounds like people may have missed the core part:

This/earlier patch are required due to select "abuse" elsewhere in the
kernel. The IS_REACHABLE/DRM_NOUVEAU_LED is patch to workaround things
on nouveau side, with a proper one to remove/untangle the "select
LEDS_CLASS". The latter will likely be slow/pain, since devs love to
use select because it's convenient (and indeed it is).
Thus [temporary] workaround on nouveau side will be good in the short term.

Afaict, "forcing LEDS to y if nouveau is set to y" is going the
opposite direction of what one should be going ;-)

Regards,
Emil