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

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Message-ID: <Yehjz1ixBKqL7Qw+@smile.fi.intel.com>
Date:   Wed, 19 Jan 2022 21:17:35 +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 Wed, Jan 19, 2022 at 11:35:22AM +0900, Esaki Tomohito wrote:
> On 2022/01/18 18:53, Andy Shevchenko wrote:
> > 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.
> 
> Ah I see. In this case, DRM_FORMAT_MOD_INVALID is terminator, so it
> should not have a comma.

Thanks for pointing this out. In this case we are good and any new item, AFAIU,
must be added before _INVALID one.

-- 
With Best Regards,
Andy Shevchenko