linux-kernel - Re: [PATCH/RFC 3/3] drm: Split drm_modeset_helper

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Date:   Fri, 29 Sep 2023 09:11:41 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH/RFC 3/3] drm: Split drm_modeset_helper_vtables.h

Hi

Am 28.09.23 um 17:32 schrieb Geert Uytterhoeven:
> Hi Thomas,
> 
> On Thu, Sep 28, 2023 at 3:59 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:
>> Am 28.09.23 um 14:16 schrieb Geert Uytterhoeven:
>>> <drm/drm_modeset_helper_vtables.h> is the second largest header file in
>>> the DRM subsystem, and declares helpers vtables for various DRM
>>> components.  Several vtables contain methods with the same name, and all
>>> but one vtable do not fit on the screen, making it hard to navigate to
>>> the actual method one is interested in.
>>>
>>> Make it easier for the casual reviewer to keep track by splitting
>>> <drm/drm_modeset_helper_vtables.h> in multiple header files, one per DRM
>>> component.
>>
>> I never liked this header either, but do we need new header files? Each
>> struct could be appended to the end of the regular header: struct
>> drm_plane_helper_funcs to drm_plane.h, drm_connector_helper_func to
>> drm_connector.h and so on.
> 
> That would work for me, too.  But perhaps we want to maintain a clear
> separation between core and helpers?
> 
> Note that moving the contents to *_helper.h would be another option,
> drm_crtc_helper.h and drm_plane_helper.h already exist.

I've taken a closer look at the users of the _vtables header. There's 
code in drm_atomic_helper.c or drm_probe_helper.c that invokes the 
callback functions.

The drivers fill the pointers with code that often comes from other 
helper modules. That code is in files like drm_plane_helper.c or 
drm_crtc_helper.c. There header files are drm_plane_helper.h, etc.

In that context, the _vtables header makes sense, as it separates the 
callers from the callees. Putting the structs into headers like 
drm_plane_helper.h would move it to the callee side.

I suggest to leave the header as it is. The fallout to the code base 
from refactoring seems worse than the current state.

Best regards
Thomas

> 
>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>>> ---
>>> RFC, a future patch could replace inclusion of
>>> <drm/drm_modeset_helper_vtables.h> by inclusion of one or more of the
>>> new files, and reduce compilation time.
>>> ---
>>>    include/drm/drm_connector_helper_vtable.h   |  364 +++++
>>>    include/drm/drm_crtc_helper_vtable.h        |  483 ++++++
>>>    include/drm/drm_encoder_helper_vtable.h     |  381 +++++
>>>    include/drm/drm_mode_config_helper_vtable.h |   97 ++
>>>    include/drm/drm_modeset_helper_vtables.h    | 1466 +------------------
>>>    include/drm/drm_plane_helper_vtable.h       |  297 ++++
>>>    6 files changed, 1627 insertions(+), 1461 deletions(-)
>>>    create mode 100644 include/drm/drm_connector_helper_vtable.h
>>>    create mode 100644 include/drm/drm_crtc_helper_vtable.h
>>>    create mode 100644 include/drm/drm_encoder_helper_vtable.h
>>>    create mode 100644 include/drm/drm_mode_config_helper_vtable.h
>>>    create mode 100644 include/drm/drm_plane_helper_vtable.h
> 
> Gr{oetje,eeting}s,
> 
>                          Geert
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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