[PATCH 1/2] of: add helper to parse display specs

[Steffen Trumtrar]

On Mon, Oct 01, 2012 at 10:53:08AM -0600, Stephen Warren wrote:
> On 09/24/2012 09:35 AM, Steffen Trumtrar wrote:
> > Parse a display-node with timings and hardware-specs from devictree.
> 
> > diff --git a/Documentation/devicetree/bindings/video/display b/Documentation/devicetree/bindings/video/display
> > new file mode 100644
> > index 0000000..722766a
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/video/display
> 
> This should be display.txt.
> 
Okay

> > @@ -0,0 +1,208 @@
> > +display bindings
> > +==================
> > +
> > +display-node
> > +------------
> 
> I'm not personally convinced about the direction this is going. While I
> think it's reasonable to define DT bindings for displays, and DT
> bindings for display modes, I'm not sure that it's reasonable to couple
> them together into a single binding.
> 
> I think creating a well-defined timing binding first will be much
> simpler than doing so within the context of a display binding; the
> scope/content of a general display binding seems much less well-defined
> to me at least, for reasons I mentioned before.
> 

Yes, you are right. I'm in the middle of moving things around a little.
It seems best, to have bindings only for the timings at the moment and
get people to agree on those and use them, instead of all the adhoc solutions
based on of_videomode v2.

Then, the of_get_display_timings and the conversion via videomode to fb_videomode
etc can be combined with Laurent Pincharts panel proposal.

> > +required properties:
> > + - none
> > +
> > +optional properties:
> > + - default-timing: the default timing value
> > + - width-mm, height-mm: Display dimensions in mm
> 
> > + - hsync-active-high (bool): Hsync pulse is active high
> > + - vsync-active-high (bool): Vsync pulse is active high
> 
> At least those two properties should exist in the display timing instead
> (or perhaps as well). There are certainly cases where different similar
> display modes are differentiated by hsync/vsync polarity more than
> anything else. This is probably more likely with analog display
> connectors than digital, but I see no reason why a DT binding for
> display timing shouldn't cover both.
> 

Yes. Will do.

> > + - de-active-high (bool): Data-Enable pulse is active high
> > + - pixelclk-inverted (bool): pixelclock is inverted
> 
> > + - pixel-per-clk
> 
> pixel-per-clk is probably something that should either be part of the
> timing definition, or something computed internally to the display
> driver based on rules for the signal type, rather than something
> represented in DT.
> 
> The above comment assumes this property is intended to represent DVI's
> requirement for pixel clock doubling for low-pixel-clock-rate modes. If
> it's something to do with e.g. a single-data-rate vs. double-data-rate
> property of the underlying physical connection, that's most likely
> something that should be defined in a binding specific to e.g. LVDS,
> rather than something generic.
> 
> > + - link-width: number of channels (e.g. LVDS)
> > + - bpp: bits-per-pixel
> > +
> > +timings-subnode
> > +---------------
> > +
> > +required properties:
> > +subnodes that specify
> > + - hactive, vactive: Display resolution
> > + - hfront-porch, hback-porch, hsync-len: Horizontal Display timing parameters
> > +   in pixels
> > +   vfront-porch, vback-porch, vsync-len: Vertical display timing parameters in
> > +   lines
> > + - clock: displayclock in Hz
> > +
> > +There are different ways of describing a display and its capabilities. The devicetree
> > +representation corresponds to the one commonly found in datasheets for displays.
> > +The description of the display and its timing is split in two parts: first the display
> > +properties like size in mm and (optionally) multiple subnodes with the supported timings.
> > +If a display supports multiple signal timings, the default-timing can be specified.
> > +
> > +Example:
> > +
> > +	display at 0 {
> > +		width-mm = <800>;
> > +		height-mm = <480>;
> > +		default-timing = <&timing0>;
> > +		timings {
> > +			timing0: timing at 0 {
> 
> If you're going to use a unit address ("@0") to ensure that node names
> are unique (which is not mandatory), then each node also needs a reg
> property with matching value, and #address-cells/#size-cells in the
> parent. Instead, you could name the nodes something unique based on the
> mode name to avoid this, e.g. 1080p24 { ... }.
> 

Ah, okay. Wasn't sure that was valid. I prefer to not use unit addresses.

 

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |