From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacek Anaszewski Subject: Re: [PATCH/RFC v10 03/19] DT: leds: Add led-sources property Date: Fri, 16 Jan 2015 10:07:28 +0100 Message-ID: <54B8D4D0.3000904@samsung.com> References: <1420816989-1808-1-git-send-email-j.anaszewski@samsung.com> <1420816989-1808-4-git-send-email-j.anaszewski@samsung.com> <54B38682.5080605@samsung.com> <54B3F1EF.4060506@samsung.com> <54B4DA81.7060900@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-reply-to: Sender: linux-leds-owner@vger.kernel.org To: Rob Herring Cc: linux-leds@vger.kernel.org, "linux-media@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" , Kyungmin Park , Bartlomiej Zolnierkiewicz , Pavel Machek , Bryan Wu , Richard Purdie , sakari.ailus@iki.fi, Sylwester Nawrocki , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Liam Girdwood , Mark Brown List-Id: devicetree@vger.kernel.org On 01/15/2015 03:24 PM, Rob Herring wrote: > On Tue, Jan 13, 2015 at 2:42 AM, Jacek Anaszewski > wrote: >> On 01/12/2015 05:55 PM, Rob Herring wrote: >>> >>> Adding Mark B and Liam... >>> >>> On Mon, Jan 12, 2015 at 10:10 AM, Jacek Anaszewski >>> wrote: >>>> >>>> On 01/12/2015 02:52 PM, Rob Herring wrote: >>>>> >>>>> >>>>> On Mon, Jan 12, 2015 at 2:32 AM, Jacek Anaszewski >>>>> wrote: >>>>>> >>>>>> On 01/09/2015 07:33 PM, Rob Herring wrote: >>>>>>> >>>>>>> On Fri, Jan 9, 2015 at 9:22 AM, Jacek Anaszewski >>>>>>> wrote: >>>>>>>> >>>>>>>> Add a property for defining the device outputs the LED >>>>>>>> represented by the DT child node is connected to. >>> >>> >>> [...] >>> >>>>>>>> b/Documentation/devicetree/bindings/leds/common.txt >>>>>>>> index a2c3f7a..29295bf 100644 >>>>>>>> --- a/Documentation/devicetree/bindings/leds/common.txt >>>>>>>> +++ b/Documentation/devicetree/bindings/leds/common.txt >>>>>>>> @@ -1,6 +1,10 @@ >>>>>>>> Common leds properties. >>>>>>>> >>>>>>>> Optional properties for child nodes: >>>>>>>> +- led-sources : Array of bits signifying the LED current regulator >>>>>>>> outputs the >>>>>>>> + LED represented by the child node is connected to (1 >>>>>>>> - >>>>>>>> the LED >>>>>>>> + is connected to the output, 0 - the LED isn't >>>>>>>> connected >>>>>>>> to the >>>>>>>> + output). >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> Sorry, I just don't understand this. >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> In some Flash LED devices one LED can be connected to one or more >>>>>> electric current outputs, which allows for multiplying the maximum >>>>>> current allowed for the LED. Each sub-LED is represented by a child >>>>>> node in the DT binding of the Flash LED device and it needs to declare >>>>>> which outputs it is connected to. In the example below the led-sources >>>>>> property is a two element array, which means that the flash LED device >>>>>> has two current outputs, and the bits signify if the LED is connected >>>>>> to the output. >>>>> >>>>> >>>>> >>>>> Sounds like a regulator for which we already have bindings for and we >>>>> have a driver for regulator based LEDs (but no binding for it). >>>> >>>> >>>> >>>> Do you think of drivers/leds/leds-regulator.c driver? This driver just >>>> allows for registering an arbitrary regulator device as a LED subsystem >>>> device. >>>> >>>> There are however devices that don't fall into this category, i.e. they >>>> have many outputs, that can be connected to a single LED or to many LEDs >>>> and the driver has to know what is the actual arrangement. >>> >>> >>> We may need to extend the regulator binding slightly and allow for >>> multiple phandles on a supply property, but wouldn't something like >>> this work: >>> >>> led-supply = <&led-reg0>, <&led-reg1>, <&led-reg2>, <&led-reg3>; >>> >>> The shared source is already supported by the regulator binding. >> >> >> I think that we shouldn't split the LED devices into power supply >> providers and consumers as in case of generic regulators. From this >> point of view a LED device current output is a provider and a discrete >> LED element is a consumer. In this approach each discrete LED element >> should have a related driver which is not how LED devices are being >> handled in the LED subsystem, where there is a single binding for a LED >> device and there is a single driver for it which creates separate LED >> class devices for each LED connected to the LED device output. Each >> discrete LED is represented by a child node in the LED device binding. >> >> I am aware that it may be tempting to treat LED devices as common >> regulators, but they have their specific features which gave a >> reason for introducing LED class for them. Besides, there is already >> drivers/leds/leds-regulator.c driver for LED devices which support only >> turning on/off and setting brightness level. >> >> In your proposition a separate regulator provider binding would have >> to be created for each current output and a separate binding for >> each discrete LED connected to the LED device. It would create >> unnecessary noise in a dts file. >> >> Moreover, using regulator binding implies that we want to treat it >> as a sheer power supply for our device (which would be a discrete LED >> element in this case), whereas LED devices provide more features like >> blinking pattern and for flash LED devices - flash timeout, external >> strobe and flash faults. > > Okay, fair enough. Please include some of this explanation in the > binding description. > > I do still have some concerns about led-sources and whether it can > support other scenarios. It is very much tied to the parent node. Are > there any cases where we don't want the LEDs to be sub nodes? Perhaps > the LEDs are on a separate daughterboard from the driver/supply and we > can have different drivers. It's a stretch maybe. I think it is. Such arrangements would introduce problems also to the other existing bindings. Probably not only LED subsystem related ones. > Or are there cases > where you need more information than just the connection? Currently I can't think of any. Modified rough proposal of the description: -Optional properties for child nodes: +LED and flash LED devices provide the same basic functionality as +current regulators, but extended with LED and flash LED specific +features like blinking patterns, flash timeout, flash faults and +external flash strobe mode. + +Many LED devices expose more than one current output that can be +connected to one or more discrete LED component. Since the arrangement +of connections can influence the way of the LED device initialization, +the LED components have to be tightly coupled with the LED device +binding. They are represented in the form of its child nodes. + +Optional properties for child nodes (if a LED device exposes only one +current output the properties can be placed directly in the LED device +node): +- led-sources : Array of connection states between all LED current + sources exposed by the device and this LED (1 - this LED + is connected to the current output with index N, 0 - + this LED isn't connected to the current output with + index N); the mapping of N-th element of the array to + the physical device output should be defined in the LED + driver binding. -- Best Regards, Jacek Anaszewski