On 10/01/2012 01:16 PM, Mitch Bradley wrote:
On 10/1/2012 6:53 AM, 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.
@@ -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.
+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.
- 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@0 {
width-mm = <800>;height-mm = <480>;default-timing = <&timing0>;timings {timing0: timing@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 { ... }.
I'm concerned that numbered nodes are being misused as arrays.
It's easy to make real arrays by including multiple cells in the value of each timing parameter, and easy to choose a cell by saying the array index instead of using the phandle.
In this case though, arrays don't work out so well in my opinion:
We want to describe a set of unrelated display modes that the display can handle. These are logically separate entities. I don't think combining the values that represent say 5 different modes into a single set of properties really makes sense here; a separate node or property per display mode really does make sense because they're separate objects.
Related, each display timing parameter (e.g. hsync length, position, ...) has a range, so min/typical/max values. These are already represented as a 3-cell property as I believe you're proposing. Combining that with a cell that represents n different modes in a single array seems like it'd end up with something rather hard to read, at least for humans even if it would be admittedly trivial for a CPU.