linux-kernel - Re: [RFC PATCH v3 2/3] drm: add support modifiers for drivers whose planes only support linear layout

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Date:   Tue, 18 Jan 2022 11:53:34 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Esaki Tomohito <etom@...l.co.jp>
Cc:     dri-devel@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Ben Skeggs <bskeggs@...hat.com>,
        Michel Dänzer <mdaenzer@...hat.com>,
        Simon Ser <contact@...rsion.fr>,
        Qingqing Zhuo <qingqing.zhuo@....com>,
        Bas Nieuwenhuizen <bas@...nieuwenhuizen.nl>,
        Mark Yacoub <markyacoub@...omium.org>,
        Sean Paul <seanpaul@...omium.org>,
        Evan Quan <evan.quan@....com>, Petr Mladek <pmladek@...e.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Lee Jones <lee.jones@...aro.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Rob Clark <robdclark@...omium.org>,
        amd-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        nouveau@...ts.freedesktop.org, Daniel Stone <daniel@...ishbar.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Damian Hobson-Garcia <dhobsong@...l.co.jp>,
        Takanari Hayama <taki@...l.co.jp>
Subject: Re: [RFC PATCH v3 2/3] drm: add support modifiers for drivers whose
 planes only support linear layout

On Mon, Jan 17, 2022 at 02:15:48PM +0900, Esaki Tomohito wrote:
> On 2022/01/14 23:16, Andy Shevchenko wrote:
> > On Fri, Jan 14, 2022 at 07:17:52PM +0900, Tomohito Esaki wrote:
> > > The LINEAR modifier is advertised as default if a driver doesn't specify
> > > modifiers.
> > 
> > ...
> > 
> > > +	const uint64_t default_modifiers[] = {
> > > +		DRM_FORMAT_MOD_LINEAR,
> > > +		DRM_FORMAT_MOD_INVALID
> > 
> > + Comma?
> 
> There is no mention in the coding style about adding/removing a comma to the
> last element of an array. Is there a policy in drm driver?
> 
> I think the advantage of adding a comma to the last element of an array is
> that diff is only one line when an element is added to the end.
> However since INVALID is always the last element in the modifiers array, I
> think it can be either in this case.
> If there is a policy, I will match it.

Indeed, but there is a common sense. The idea behind (multi-line) definitions
that when next time somebody will add an element in the array, there are will
be:

a) no additional churn (like in case of this patch, if the item will be added
   at the bottom;

b) an element that may not be added behind the terminator, which will look
   weird.

That said, the question is if the element is terminator one or not, if not,
comma is better than no comma and vise versa.

-- 
With Best Regards,
Andy Shevchenko