Re: [PATCH v2 07/19] tegra: fdt: Add LCD definitions for Tegra

From: Thierry Reding <thierry.reding@avionic-design.de>
To: Simon Glass <sjg@chromium.org>
Cc: Stephen Warren <swarren@nvidia.com>,
	Devicetree Discuss <devicetree-discuss@lists.ozlabs.org>,
	U-Boot Mailing List <u-boot@lists.denx.de>,
	Jerry Van Baren <vanbaren@cideas.com>,
	Alex Courbot <acourbot@nvidia.com>,
	Tom Warren <twarren@nvidia.com>
Subject: Re: [PATCH v2 07/19] tegra: fdt: Add LCD definitions for Tegra
Date: Thu, 12 Jul 2012 10:40:51 +0200	[thread overview]
Message-ID: <20120712084051.GA27022@avionic-0098.adnet.avionic-design.de> (raw)
In-Reply-To: <CAPnjgZ0Lv2rjVzNottsY+NWYmred5Au+hebUuTTOSAJufTkLjA@mail.gmail.com>

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On Thu, Jul 12, 2012 at 10:21:01AM +0200, Simon Glass wrote:
> Hi Thierry,
> 
> On Wed, Jul 11, 2012 at 7:48 AM, Thierry Reding
> <thierry.reding@avionic-design.de> wrote:
> > On Wed, Jul 11, 2012 at 06:44:10AM +0200, Simon Glass wrote:
> >> Hi Stephen,
> >>
> >> On Fri, Jun 15, 2012 at 1:32 AM, Stephen Warren <swarren@wwwdotorg.org>wrote:
> >>
> >> > On 06/13/2012 10:19 AM, Simon Glass wrote:
> >> > > Add LCD definitions and also a proposed binding for LCD displays.
> >> > >
> >> > > The PWFM is in progress on the device-tree-discuss list, so only a
> >> > > very basic binding is offered here.
> >> >
> >> > I believe we have settled on a final representation, it just hasn't been
> >> > added into linux-next yet. See:
> >> >
> >> >
> >> > http://gitorious.org/linux-pwm/linux-pwm/commit/d3ce73e5dc86646a6302f2b0f7dd40e8c552fa04
> >>
> >>
> >> Thanks for the pointer. I suppose this doesn't address clocks as yet, but
> >> that's fine.
> >
> > I was waiting for the common clock framework and DT bindings to get
> > ready. This should happen RSN for Tegra so I will probably look at
> > adding support for it in.
> 
> OK, are you looking at adding it in U-Boot?

No. I don't have much time to spend on U-Boot right now.

[...]
> I also need a place to put the pwm and GPIOs for the panel itself.
> Something like this:
> 
> 		nvidia,pwm = <&pwm 2 0>;
> 		nvidia,backlight-enable-gpios = <&gpio 28 0>;	/* PD4 */
> 		nvidia,lvds-shutdown-gpios = <&gpio 10 0>;	/* PB2 */
> 		nvidia,backlight-vdd-gpios = <&gpio 176 0>;	/* PW0 */
> 		nvidia,panel-vdd-gpios = <&gpio 22 0>;		/* PC6 */
> 		nvidia,panel-timings = <4 203 17 15>;  (number of ms before turning
> on the next gpio)
> 		nvidia,bits-per-pixel = <16>;    (er, TBD)
> 
> I am thinking of something like a phandle in your rgb node:
> 
> 	host1x {
> 		dc@54200000 {
> 			rgb {
> 				nvidia-panel = <&lcd_panel>;
> ...
> 
> 	lcd_panel: panel {
> 		nvidia,pwm = <&pwm 2 0>;
>                 ...
>         }
> 
> Or have you already solved this problem another way?

Linux has a generic PWM backlight driver. This is currently solved by
using this in the DT:

	backlight {
		compatible = "pwm-backlight";
		pwms = <&pwm 0 5000000>;

		brightness-levels = <0 4 8 16 32 64 128 255>;
		default-brightness-level = <6>;
	};

Alex Courbot (Cc'd) has been working on adding a generic way to add GPIO
and regulator support to that. I don't know exactly what the
lvds-shutdown-gpios and panel-vdd-gpios properties do. If they control
hardware connected behind the display controller I suppose they could go
into the rgb node.

The panel alternative that you propose sounds interesting as well. Maybe
the panel should itself contain either a phandle or a subnode for the
backlight and collect the properties that you listed above.

Thierry

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