Leds

Leds

[Marco Stornelli]

Hi all,

how can specify a led device in a dts file? These leds are connected
with gpio to the microprocessor. I can't find anything like a led node
in the dts files of the other boards. Have you got any suggestions?

Regards,

Marco

Re: Leds

[Simon Kagstrom]

Hi Marco,

On Fri, 08 Feb 2008 11:02:16 +0100
Marco Stornelli <marco.stornelli@coritel.it> wrote:

> how can specify a led device in a dts file? These leds are connected
> with gpio to the microprocessor. I can't find anything like a led node
> in the dts files of the other boards. Have you got any suggestions?

Although I'm not sure if it's the "standard" way, we just added a
"home-made" node like this:

	resetLED@c0018000 {
		device_type = "leds";
		compatible = "reset-leds";
		reg = <c0018000 00008000>;
	};

and then just get the info in the probe function for the led driver
we placed in drivers/leds/:

	/* Get device info from OF tree */
	np = of_find_compatible_node(NULL, "leds", "reset-leds");
	if (!np) {
		dev_err(&pdev->dev, "Could not find device tree node for reset-leds\n");
		goto error_classdev;
	}

	if (of_address_to_resource(np, 0, &res)) {
		dev_err(&pdev->dev, "Could not convert reset-leds device tree address\n");
		of_node_put(np);
		goto error_classdev;
	}
	...

At least this was all the information we needed from the device tree.

// Simon

Re: Leds

[Marco Stornelli]

Simon Kagstrom ha scritto:
> Hi Marco,
> 
> On Fri, 08 Feb 2008 11:02:16 +0100
> Marco Stornelli <marco.stornelli@coritel.it> wrote:
> 
>> how can specify a led device in a dts file? These leds are connected
>> with gpio to the microprocessor. I can't find anything like a led node
>> in the dts files of the other boards. Have you got any suggestions?
> 
> Although I'm not sure if it's the "standard" way, we just added a
> "home-made" node like this:
> 
> 	resetLED@c0018000 {
> 		device_type = "leds";
> 		compatible = "reset-leds";
> 		reg = <c0018000 00008000>;
> 	};
> 
> and then just get the info in the probe function for the led driver
> we placed in drivers/leds/:
> 
> 	/* Get device info from OF tree */
> 	np = of_find_compatible_node(NULL, "leds", "reset-leds");
> 	if (!np) {
> 		dev_err(&pdev->dev, "Could not find device tree node for reset-leds\n");
> 		goto error_classdev;
> 	}
> 
> 	if (of_address_to_resource(np, 0, &res)) {
> 		dev_err(&pdev->dev, "Could not convert reset-leds device tree address\n");
> 		of_node_put(np);
> 		goto error_classdev;
> 	}
> 	...
> 
> At least this was all the information we needed from the device tree.
> 
> // Simon
> 

Thanks. In this case where have you added the device registration? In
the probe function? Have you registered the driver with
of_register_platform_driver()?

Re: Leds

[Simon Kagstrom]

On Fri, 08 Feb 2008 11:43:25 +0100
Marco Stornelli <marco.stornelli@coritel.it> wrote:

> > Although I'm not sure if it's the "standard" way, we just added a
> > "home-made" node like this:
> > 
> > 	resetLED@c0018000 {
> > 		device_type = "leds";
> > 		compatible = "reset-leds";
> > 		reg = <c0018000 00008000>;
> > 	};
> > 
> Thanks. In this case where have you added the device registration? In
> the probe function? Have you registered the driver with
> of_register_platform_driver()?

We put it in the module init function and registered it as a platform
device:

static int __init led_init(void)
{
	int ret;

	ret = platform_driver_register(&led_driver);

	if (ret < 0)
		return -ENODEV;

	pdev = platform_device_register_simple(DRVNAME, -1, NULL, 0);
	if (IS_ERR(pdev)) {
		ret = PTR_ERR(pdev);
		platform_driver_unregister(&led_driver);
	}

	return ret;
}

And just use the device tree stuff to read out the device address. The
driver itself is quite similar to other led drivers found in the same
directory, so you can probably base your work on those.

This was for kernel 2.6.21, I'm not sure if these things have changed
for newer kernels (although I would guess most of it is the same).

// Simon

Re: Leds

[Grant Likely]

On Feb 8, 2008 3:20 AM, Simon Kagstrom <simon.kagstrom@ericsson.com> wrote:
> Hi Marco,
>
> On Fri, 08 Feb 2008 11:02:16 +0100
> Marco Stornelli <marco.stornelli@coritel.it> wrote:
>
> > how can specify a led device in a dts file? These leds are connected
> > with gpio to the microprocessor. I can't find anything like a led node
> > in the dts files of the other boards. Have you got any suggestions?
>
> Although I'm not sure if it's the "standard" way, we just added a
> "home-made" node like this:
>
>         resetLED@c0018000 {
>                 device_type = "leds";
>                 compatible = "reset-leds";
>                 reg = <c0018000 00008000>;
>         };

I've been thinking about this a bit over the last couple of months,
and I think that there is a better way.  Since many LEDs are simply
hooked up to GPIO blocks and we're moving towards a common GPIO api
(and device tree binding), I think it would be better to use two
nodes; a node for the gpio block and a node for all the LEDs in the
system.  For example (the GPIO dt bindings may differ from my example
here, but you get the gist):

GPIO0: gpio-controller@1418 {
        #gpio-cells = <2>;
        compatible = "fsl,qe-pario-bank";
        reg = <0x1418 0x18>;
        gpio-controller;
};
GPIO1: gpio-controller@1460 {
        #gpio-cells = <2>;
        compatible = "fsl,qe-pario-bank";
        reg = <0x1460 0x18>;
        gpio-controller;
};

leds@0 {
        compatible = "gpio-leds";
        led-labels = "led1", "led2", "led3", "led4";
        gpios = <&GPIO0  2 0 /* LED1 */
                 &GPIO0  3 0 /* LED2 */
                 &GPIO1  8 0 /* LED3 */
                 &GPIO1  9 0 /* LED4 */
                 >;
        /* More properties are probably needed here to correctly setup
the output levels */
};

Doing it this way means the GPIO block will be usable for more than
just LEDs.  Plus once the 'gpio-leds' driver is written leds can be
hooked up almost trivially on new boards.

Cheers,
g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.