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: Tue, 20 Jan 2015 17:09:15 +0100 Message-ID: <54BE7DAB.80702@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> <54B8D4D0.3000904@samsung.com> <54B933D0.1090004@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-reply-to: <54B933D0.1090004@samsung.com> 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 01/16/2015 04:52 PM, Jacek Anaszewski wrote: > On 01/16/2015 02:48 PM, Rob Herring wrote: >> On Fri, Jan 16, 2015 at 3:07 AM, Jacek Anaszewski >> wrote: >>> 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): >> >> Why special case 1 output case? Just always require a child node. > > OK. > >>> +- 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. >> >> I think this should be a list of connected output numbers rather than >> effectively a bitmask. >> >> You may want to add something like led-output-cnt or led-driver-cnt in >> the parent so you know the max list size. > > Why should we need this? The number of current outputs exposed by the > device is fixed and can be specified in a LED device bindings > documentation. > OK. The led-output-cnt property should be put in each sub-node, as the number of the current outputs each LED can be connected to is variable. New version: Optional properties for child nodes: +led-sources-cnt : Number of device current outputs the LED is connected to. +- led-sources : List of device current outputs the LED is connected to. The + outputs are identified by the numbers that must be defined + in the LED device binding documentation. - label : The label for this LED. If omitted, the label is taken from the node name (excluding the unit address). @@ -33,7 +47,9 @@ system-status { camera-flash { label = "Flash"; + led-sources-cnt = <2>; + led-sources = <0>, <1>; max-microamp = <50000>; flash-max-microamp = <320000>; flash-timeout-us = <500000>; -} +}; -- Best Regards, Jacek Anaszewski