linux-kernel - Re: [PATCH] drm/ssd130x: Drop _helper prefix from struct drm_*_helper

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Message-ID: <878r90kk8h.fsf@minerva.mail-host-address-is-not-set>
Date:   Thu, 21 Sep 2023 10:23:42 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <mripard@...nel.org>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/ssd130x: Drop _helper prefix from struct
 drm_*_helper_funcs callbacks

Geert Uytterhoeven <geert@...ux-m68k.org> writes:

Hello Geert and Maxime,

> Hi Maxime,
>
> On Thu, Sep 21, 2023 at 9:44 AM Maxime Ripard <mripard@...nel.org> wrote:
>> On Mon, Sep 18, 2023 at 09:19:07AM +0200, Javier Martinez Canillas wrote:
>> > Thomas Zimmermann <tzimmermann@...e.de> writes:
>> > > Am 14.09.23 um 21:51 schrieb Javier Martinez Canillas:
>> > >> The driver uses a naming convention where functions for struct drm_*_funcs
>> > >> callbacks are named ssd130x_$object_$operation, while the callbacks for
>> > >> struct drm_*_helper_funcs are named ssd130x_$object_helper_$operation.
>> > >>
>> > >> The idea is that this helper_ prefix in the function names denote that are
>> > >> for struct drm_*_helper_funcs callbacks. This convention was copied from
>> > >> other drivers, when ssd130x was written but Maxime pointed out that is the
>> > >> exception rather than the norm.
>> > >
>> > > I guess you found this in my code. I want to point out that I use the
>> > > _helper infix to signal that these are callback for
>> > > drm_primary_plane_helper_funcs and *not* drm_primary_plane_funcs. The
>> > > naming is intentional.
>> >
>> > Yes, that's what tried to say in the commit message and indeed I got the
>> > convention from drivers in drivers/gpu/drm/tiny. In fact I believe these
>> > function names are since first iteration of the driver, when was meant to
>> > be a tiny driver.
>> >
>> > According to Maxime it's the exception rather than the rule and suggested
>> > to change it, I don't really have a strong opinion on either naming TBH.
>>
>> Maybe that's just me, but the helper in the name indeed throws me off. In my
>> mind, it's supposed to be used only for helpers, not functions implementing the
>> helpers hooks.

I agree with your definition of helpers. But more importantly for me is
what you mentioned, that most DRM drivers aren't using this convention
of concatenating  the driver name + struct type name + callback name.

>
> With several callbacks using the same (field) name, it is very helpful
> to name the actual implementation by combining the struct type name
> and the field name.  Anything else confuses the casual reader.

Both options have cons and pros (e.g: quickly figuring out to what struct
callback is associated as you said), but the reason I posted this patch is
to attempt making the driver more consistent with the rest of the drivers.

> Perhaps the real question is whether the structures should have "helper"
> in their name in the first place?
>

Indeed. I never fully understood why the DRM/KMS objects callbacks are
split in drm_$object_funcs and drm_$object_helper_funcs structs. AFAIU
is because the former is the minimum required and the latter is to add
additional custom behavior ?

I read this section of the documentation but still isn't clear to me:

https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html

> Just my 2€c as a DRM novice...
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat