From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Herring Subject: Re: [PATCH 4/6] dt-bindings: display: armada: Add display subsystem binding Date: Mon, 21 Jan 2019 10:07:11 -0600 Message-ID: References: <20190120172534.24617-1-lkundrak@v3.sk> <20190120172534.24617-5-lkundrak@v3.sk> <3191cdde84978adf98d200a9db6f3c18e0a46390.camel@v3.sk> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <3191cdde84978adf98d200a9db6f3c18e0a46390.camel@v3.sk> Sender: linux-kernel-owner@vger.kernel.org To: Lubomir Rintel Cc: Mark Rutland , Russell King , dri-devel , devicetree@vger.kernel.org, "linux-kernel@vger.kernel.org" List-Id: dri-devel@lists.freedesktop.org On Mon, Jan 21, 2019 at 9:46 AM Lubomir Rintel wrote: > > On Mon, 2019-01-21 at 09:35 -0600, Rob Herring wrote: > > On Sun, Jan 20, 2019 at 11:26 AM Lubomir Rintel wrote: > > > The Marvell Armada DRM master device is a virtual device needed to list all > > > nodes that comprise the graphics subsystem. > > > > > > Signed-off-by: Lubomir Rintel > > > --- > > > .../display/armada/marvell-armada-drm.txt | 24 +++++++++++++++++++ > > > 1 file changed, 24 insertions(+) > > > > > > diff --git a/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt b/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt > > > index de4cca9432c8..3dbfa8047f0b 100644 > > > --- a/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt > > > +++ b/Documentation/devicetree/bindings/display/armada/marvell-armada-drm.txt > > > @@ -1,3 +1,27 @@ > > > +Marvell Armada DRM master device > > > +================================ > > > + > > > +The Marvell Armada DRM master device is a virtual device needed to list all > > > +nodes that comprise the graphics subsystem. > > > + > > > +Required properties: > > > + > > > + - compatible: value should be "marvell,dove-display-subsystem", > > > + "marvell,armada-display-subsystem" > > > + - ports: a list of phandles pointing to display interface ports of CRTC > > > + devices > > > + - memory-region: phandle to a node describing memory to be used for the > > > + framebuffer > > > + > > > +Example: > > > + > > > + display-subsystem { > > > + compatible = "marvell,dove-display-subsystem", > > > + "marvell,armada-display-subsystem"; > > > + memory-region = <&display_reserved>; > > > + ports = <&lcd0_port>; > > > > If there is only one device, you don't need this virtual node. > > By "one device" you mean one LCD controller (CRTC)? Yes. > I suppose in the (single CRTC) example case, the display-subsystem node > used to associate it with the memory region reserved for allocating the > frame buffers from. Could that be done differently? Move memory-region to the LCD controller node. > Also, if the node is indeed made optional, then it's going to > complicate things on the DRM side. Currently the driver that binds to > the node creates the DRM device once it sees all the components > connected to the ports appear. If we loose it, then the LCD controller > driver would somehow need to find out that it's alone and create the > DRM device itself. DT is not the only way to create devices. The DRM driver can bind to the LCDC node and then create a child CRTC device (or even multiple ones for h/w with multiple pipelines). You'll also notice that there are only 3 cases of this virtual node in the tree: STi, i.MX IPU, and Rockchip. That's because we've deprecated doing these virtual nodes for some time now. IOW, there are several examples of how to do this without a virtual node. Rob