On Sun, Jan 19, 2014 at 11:03:24AM -0800, Olof Johansson wrote: > [Adding devicetree list since we're talking bindings] > > On Sun, Jan 19, 2014 at 04:49:57PM +0000, Russell King - ARM Linux wrote: > > So, having looked at what else I can add support for on the cubox-i, I > > decided it would be nice and simple to add support for the front panel > > LED. What could possibly go wrong with this. > > > > Well, the hardware is wired such that the LED is connected between the > > PWM output and +3.3v. So, a constant low turns the LED on full, whereas > > a constant high turns the LED off. > > > > So, the polarity of the LED is inverted - but this _can't_ be specified > > in the totally and utterly fucked misdesigned crap that DT is: > > > > pwmleds { > > compatible = "pwm-leds"; > > pinctrl-names = "default"; > > pinctrl-0 = <&pinctrl_cubox_i_pwm1>; > > > > front { > > label = "imx6:red:front"; > > pwms = <&pwm1 0 50000>; > > max-brightness = <248>; > > }; > > }; > > > > pwm1: pwm@02080000 { > > #pwm-cells = <2>; > > compatible = "fsl,imx6q-pwm", "fsl,imx27-pwm"; > > reg = <0x02080000 0x4000>; > > interrupts = <0 83 0x04>; > > clocks = <&clks 62>, <&clks 145>; > > clock-names = "ipg", "per"; > > }; > > > > Yes, because iMX6 specifies #pwm-cells as 2, there's no flags able to > > be specified in the pwms declaration in pwmleds. So that doesn't work. > > There's no property to tell pwmleds that it should use inverted sense > > either. > > Adding a property for active-low to the pwm-leds binding would be > easy, and backwards compatible. I'm surprised the original binding > didn't specify it. The leds-pwm driver already seems to support it for > C-configured instances. > > I'm also surprised that the imx pwm driver even has a #pwm-cells of > two, since the driver only supports one output. It'd be nice if they > had allocated the extra cell for flags, but it's hard to change now, > unless you do a new binding/compatible value and deprecate the old one. > > > Moreover, there's no way to specify a default brightness for the LED > > in the absence of any trigger, so this results in the LED being fully > > on. > > That seems to be missing from the led-pwm driver altogether, not just the DT > bindings? Shouldn't be too bad to add a default-brightness property and plumb > that up through the driver in this case. > > > So, something which _should_ be nice and simple is turned into a major > > fuckup because of the total and utter crappiness that DT is and the > > total misdesign that this shite is. > > It's not a major fuckup. None of the above is unfixable. Indeed, and we already have a patch for this: http://comments.gmane.org/gmane.linux.ports.arm.kernel/294823 Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html