linux-kernel - Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for analogix

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Date:	Tue, 25 Aug 2015 11:12:48 +0200
From:	Thierry Reding <treding@...dia.com>
To:	Rob Herring <robherring2@...il.com>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Yakir Yang <ykk@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Jingoo Han <jingoohan1@...il.com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Inki Dae <inki.dae@...sung.com>, Joe Perches <joe@...ches.com>,
	Sean Paul <seanpaul@...gle.com>, Takashi Iwai <tiwai@...e.de>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Andrzej Hajda <a.hajda@...sung.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Vincent Palatin <vpalatin@...omium.org>,
	<linux-rockchip@...ts.infradead.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	David Airlie <airlied@...ux.ie>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Doug Anderson <dianders@...gle.com>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Yao <mark.yao@...k-chips.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Daniel Kurtz <djkurtz@...gle.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Kumar Gala <galak@...eaurora.org>,
	Ajay kumar <ajaynumb@...il.com>,
	Andy Yan <andy.yan@...k-chips.com>
Subject: Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for
 analogix_dp

On Mon, Aug 24, 2015 at 09:48:27AM -0500, Rob Herring wrote:
> On Mon, Aug 24, 2015 at 7:57 AM, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > On Sun, Aug 23, 2015 at 06:23:14PM -0500, Rob Herring wrote:
> >> On Wed, Aug 19, 2015 at 9:50 AM, Yakir Yang <ykk@...k-chips.com> wrote:
> >> > +       -analogix,color-depth:
> >> > +               number of bits per colour component.
> >> > +                       COLOR_6 = 0, COLOR_8 = 1, COLOR_10 = 2, COLOR_12 = 3
> >>
> >> This seems pretty generic. Just use 6, 8, 10, or 12 for values. And
> >> drop the vendor prefix.
> >
> > Please think about this some more.  What does "color-depth" mean?  Does it
> > mean the number of bits per colour _component_, or does it mean the total
> > number of bits to represent a particular colour.  It's confusing as it
> > stands.
> 
> Then "component-color-bpp" perhaps?

There should be no need to have this in DT at all. The BPC is a property
of the attached panel and it should come from the panel (either the
panel driver or parsed from EDID if available).

> > When we adopted the graph bindings for iMX DRM, I thought exactly at that
> > time "it would be nice if this could become the standard for binding DRM
> > components together" but I don't have the authority from either the DT
> > perspective or the DRM perspective to mandate that.  Neither does anyone
> > else.  That's the _real_ problem here.
> >
> > I've seen several DRM bindings go by which don't use the of-graph stuff,
> > which means that they'll never be compatible with generic components
> > which do use the of-graph stuff.
> 
> It goes beyond bindings IMO. The use of the component framework or not
> has been at the whim of driver writers as well. It is either used or
> private APIs are created. I'm using components and my need for it
> boils down to passing the struct drm_device pointer to the encoder.
> Other components like panels and bridges have different ways to attach
> to the DRM driver.

I certainly support unification, but it needs to be reasonable. There
are cases where a different structure for the binding work better than
another and I think this always needs to be evaluated on a case by case
basis.

Because of that I think it makes sense to make all these framework bits
opt-in, otherwise we could easily end up in a situation where drivers
have to be rearchitected (or even DT bindings altered!) in order to be
able to reuse code.

Thierry

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