On April 22, 2016 3:09:35 PM CEST, Rob Herring <robh@xxxxxxxxxx> wrote: >On Fri, Apr 22, 2016 at 7:38 AM, Olliver Schinagl <oliver@xxxxxxxxxxx> >wrote: >> Hey Rob, >> >> On 21-04-16 17:07, Rob Herring wrote: >>> >>> On Tue, Apr 19, 2016 at 09:40:49AM +0200, Olliver Schinagl wrote: >>>> >>>> When leds are connected in a totem-pole configuration, they can be >>>> connected either in a active-high, or active-low manor. The driver >>>> currently always assumes active-high. This patch adds the >>>> 'nxp,inverted-out' boolean property to tell the driver that the >leds >>>> are driven active-low, or rather, that the behavior is inverted to >what >>>> is normally expected. >>> >>> How do I know what is normally expected? >> >> fair point, and in fact, you don't. The text is bad here. > >The problem is not so much the text here, but the property is also >meaningless without some explanation. > Well the datasheet states only that it will invert the output. So would it make sense to just state the same here? >>> >>> >>>> Signed-off-by: Olliver Schinagl <oliver@xxxxxxxxxxx> >>>> --- >>>> Documentation/devicetree/bindings/leds/pca963x.txt | 1 + >>>> drivers/leds/leds-pca963x.c | 20 >>>> +++++++++++++------- >>>> include/linux/platform_data/leds-pca963x.h | 1 + >>>> 3 files changed, 15 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/Documentation/devicetree/bindings/leds/pca963x.txt >>>> b/Documentation/devicetree/bindings/leds/pca963x.txt >>>> index dafbe99..7b23725 100644 >>>> --- a/Documentation/devicetree/bindings/leds/pca963x.txt >>>> +++ b/Documentation/devicetree/bindings/leds/pca963x.txt >>>> @@ -6,6 +6,7 @@ Required properties: >>>> Optional properties: >>>> - nxp,totem-pole : use totem pole (push-pull) instead of >open-drain >>>> (pca9632 defaults >>>> to open-drain, newer chips to totem pole) >>>> + nxp,inverted-out: the connected leds are active-low, default to >>>> active-high >>> >>> Just state what mode you want: nxp,active-low >> >> But that's not what happens, which is why my text is bad :) It >depends on >> how the board is wired and if it is push-pull or open-drain. Though >this >> goes beyond my electronics knowledge. So I'll reduce the text to say >exactly >> what we mean, inverted output (or not). >> >> Unless you can explain that it would be unrelated and it is actually >> active-high/low. I'll be more than happy to oblige. > >I'm not familiar with this chip, but googling for "active low LED >circuit" can give you lots of examples. To put it simply, you are >defining whether the control/switch is on the cathode or anode side of >the LED. Open-drain vs. push-pull is also related to how the circuit >is done, but is probably an independent property. I'd think the only >reason you would use open-drain here is if you wanted to control the >LED from 2 different signals. Whether you wanted the controls to >function as OR or AND logic to turn on would determine what the active >state needs to be. I was thinking that the output behaves differently depending whether it is configured as push-pull or open-drain. So to summarize, does the output always go into active-low mode, or does it depend on other parameters as well? Olliver > >Rob -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- 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
