Re: [PATCH v4] of: Add videomode helper

Hi Rob,

On Mon, Sep 24, 2012 at 08:42:12AM -0500, Rob Herring wrote:

On 09/19/2012 03:20 AM, Steffen Trumtrar wrote:

quoted

This patch adds a helper function for parsing videomodes from the devicetree.
The videomode can be either converted to a struct drm_display_mode or a
struct fb_videomode.

+
+Required properties:
+ - 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

A major piece missing is the LCD controller to display interface width
and component ordering.

Psst. We silently skipped this for now...

I think having such a videomode helper is useful without having the
data order part. We are aware that this should be added later, but
I think currently it makes sense to concentrate on the basics.

quoted

+
+Optional properties:
+ - 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
+ - interlaced (bool): This is an interlaced mode
+ - doublescan (bool): This is a doublescan mode
+
+There are different ways of describing a display mode. The devicetree representation
+corresponds to the one commonly found in datasheets for displays.
+The description of the display and its mode is split in two parts: first the display
+properties like size in mm and (optionally) multiple subnodes with the supported modes.
+
+Example:
+
+	display@0 {

It would be useful to have a compatible string here. We may not always
know the panel type or have a fixed panel though. We could define
"generic-lcd" or something for cases where the panel type is unknown.

We expect the display nodes being subnodes of a driver (which of course
has a compatible), or maybe referred to from a driver using phandles. So
I don't see why the display node itself should have a compatible
property. The display information is only ever useful in the context of
a driver.

Sascha

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