Re: [RFC v2 PATCH v4 09/14] ARM: dts: s6e3fa0: add DT bindings

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Andrzej,

On Wednesday 23 April 2014 11:02:21 Andrzej Hajda wrote:
> On 04/21/2014 02:28 PM, YoungJun Cho wrote:
> > This patch adds DT bindings for s6e3fa0 panel.
> > The bindings describes panel resources, display timings and cpu timings.
> > 
> > Changelog v2:
> > - Adds unit address (commented by Sachin Kamat)
> > Changelog v3:
> > - Removes optional delay, size properties (commented by Laurent Pinchart)
> > - Adds OLED detection, TE gpio properties
> > Changelog v4:
> > - Moves CPU timings relevant properties from FIMD DT
> > 
> >   (commeted by Laurent Pinchart, Andrzej Hajda)
> > 
> > Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
> > Acked-by: Inki Dae <inki.dae@samsung.com>
> > Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
> > ---
> > 
> >  .../devicetree/bindings/panel/samsung,s6e3fa0.txt  |   63 +++++++++++++++
> > 1 file changed, 63 insertions(+)
> >  create mode 100644
> >  Documentation/devicetree/bindings/panel/samsung,s6e3fa0.txt> 
> > diff --git a/Documentation/devicetree/bindings/panel/samsung,s6e3fa0.txt
> > b/Documentation/devicetree/bindings/panel/samsung,s6e3fa0.txt new file
> > mode 100644
> > index 0000000..9eeb38b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/panel/samsung,s6e3fa0.txt
> > @@ -0,0 +1,63 @@
> > +Samsung S6E3FA0 AMOLED LCD 5.7 inch panel
> > +
> > +Required properties:
> > +  - compatible: "samsung,s6e3fa0"
> > +  - reg: the virtual channel number of a DSI peripheral
> > +  - vdd3-supply: core voltage supply
> > +  - vci-supply: voltage supply for analog circuits
> > +  - reset-gpio: a GPIO spec for the reset pin
> > +  - det-gpio: a GPIO spec for the OLED detection pin
> > +  - te-gpio: a GPIO spec for the TE pin
> > +  - display-timings: timings for the connected panel as described by [1]
> 
> Which properties of display-timings are relevant for CPU mode?
> I guess width and height. Anything more?
> 
> > +  - cpu-timings: CPU interface timings for the connected panel, and it
> > contains
> > +        following optional properties.
> > +          - cs-setup: clock cycles for the active period of address
> > signal
> > +                enable until chip select is enable in CPU interface
> > +          - wr-setup: clock cycles for the active period of CS signal
> > enable
> > +                until write signal is enable in CPU interface
> > +          - wr-act: clock cycles for the active period of CS enable in
> > CPU
> > +                interface

What about calling this property wr-active ? I had called this wr-cycle in a 
previous implementation, that could be an option as well.

> > +          - wr-hold: clock cycles for the active period of CS disable
> > until
> > +                write signal is disable in CPU interface
> 
> cpu-timings name does not sound to be related to display.
> I wonder if it would not be better to merge cpu-timings into
> display-timings but this will require more discussion I guess.

The panel has a memory-like interface with chip select, read/write and access 
strobe, address (1 bit) and data signals. The interface is defined in the MIPI 
DBI specification (a quick search turned up 
http://www.scribd.com/doc/206899854/MIPI-DPI-Specification-v2, there might be 
direct PDF downloads available), even if some panels implement a similar 
interface that predates MIPI DBI (with names such as i80 or SYS-80 probably 
due to the similarities with the 8051 external bus).

The cpu-timings properties describe the read and write access timings for 
those signals, unrelated to the display video timings. I thus believe that 
they should be separate from the display timings. We will probably need to add 
properties for the read signal as well, but that can be done later.

> If you want to stay with separate node please consider to make it
> optional as whole node or make some properties required. Making node
> required with all sub-properties optional is weird.
> By the way I hope all timings properties are generic for CPU mode,
> if not they should be prefixed by vendor or model.

The timings description should be pretty generic I believe, especially given 
that the interface is standardized by the MIPI alliance. Could you have a 
quick look at the spec and share your opinion ?

> > +
> > +Optional properties:
> > +
> > +The device node can contain one 'port' child node with one child
> > +'endpoint' node, according to the bindings defined in [2]. This
> > +node should describe panel's video bus.
> > +
> > +[1]: Documentation/devicetree/bindings/video/display-timing.txt
> > +[2]: Documentation/devicetree/bindings/media/video-interfaces.txt
> > +
> > +Example:
> > +
> > +	panel@0 {
> > +		compatible = "samsung,s6e3fa0";
> > +		reg = <0>;
> > +		vdd3-supply = <&vcclcd_reg>;
> > +		vci-supply = <&vlcd_reg>;
> > +		reset-gpio = <&gpy7 4 0>;
> > +		det-gpio = <&gpg0 6 0>;
> > +		te-gpio = <&gpd1 7 0>;
> > +
> > +		display-timings {
> > +			timing0: timing-0 {
> > +				clock-frequency = <0>;
> > +				hactive = <1080>;
> > +				vactive = <1920>;
> > +				hfront-porch = <2>;
> > +				hback-porch = <2>;
> > +				hsync-len = <1>;
> > +				vfront-porch = <1>;
> > +				vback-porch = <4>;
> > +				vsync-len = <1>;
> > +			};
> > +		};
> > +
> > +		cpu-timings {
> > +			cs-setup = <0>;
> > +			wr-setup = <0>;
> > +			wr-act = <1>;
> > +			wr-hold = <0>;
> > +		};
> > +	};

-- 
Regards,

Laurent Pinchart