On 10/1/2012 10:25 AM, Stephen Warren wrote: > 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. That argument seems pretty dependent on how you choose to look at things. > > 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. That argument is better. > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel