On Mon, Apr 07, 2014 at 10:46:51AM +0200, Alexandre Belloni wrote: > (adding Thierry Reding) > > Hi, > > On 06/04/2014 at 23:20:18 +0100, Russell King wrote : > > Some PWM outputs are wired such that the LED they're controlling is > > connected to supply rather than ground. These PWMs may not support > > output inversion, or when they do, disabling the PWM may set the > > PWM output low, causing a "brightness" value of zero to turn the LED > > fully on. > > > > The platform data for this driver already indicates that this was > > thought about, and we have the "active_low" property there already. > > However, the implementation for this is missing. > > > > Add the trivial implementation for this feature. > > > > Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> > > --- > > drivers/leds/leds-pwm.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c > > index e1b4c23a409a..1d47742c551f 100644 > > --- a/drivers/leds/leds-pwm.c > > +++ b/drivers/leds/leds-pwm.c > > @@ -70,6 +70,10 @@ static void led_pwm_set(struct led_classdev *led_cdev, > > > > duty *= brightness; > > do_div(duty, max); > > + > > + if (led_dat->active_low) > > + duty = led_dat->period - duty; > > + > > led_dat->duty = duty; > > > > This will conflict with my patch (which is still lacking proper review) > there: > http://thread.gmane.org/gmane.linux.leds/482 > > I would say that it is better to hide the polarity inversion in the PWM > driver for your specific PWM. Else we will end up with all the drivers > using PWMs trying to detect whether the PWM supports inversion and if it > is not the case, calculating the inverted duty cycle. > > So, I would go for my patch which is adding the missing polarity > inversion setting when using platform data and then implement software > polarity inversion in your underlying PWM driver. That also avoids patch > 5/5 and I believe not adding a DT property is always a good idea. > > What is your PWM that is not supporting polarity inversion ? Did you read the commit message properly, particularly the last sentence of the first paragraph which refers to the problem with your approach? -- FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly improving, and getting towards what was expected from it. -- To unsubscribe from this list: send the line "unsubscribe linux-leds" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
