On 07.05.2013 17:07, Laurent Pinchart wrote: > On Tuesday 07 May 2013 02:11:27 Kim, Milo wrote: >> On Monday, May 06, 2013 6:34 PM Andrzej Hajda wrote: >>> This RFC proposes generic API for exposing flash subdevices via LED >>> framework. >>> >>> Rationale >>> >>> Currently there are two frameworks which are used for exposing LED >>> flash to user space: >>> - V4L2 flash controls, >>> - LED framework(with custom sysfs attributes). >>> >>> The list below shows flash drivers in mainline kernel with initial >>> commit date and typical chip application (according to producer): >>> >>> LED API: >>> lm3642: 2012-09-12, Cameras >>> lm355x: 2012-09-05, Cameras >>> max8997: 2011-12-14, Cameras (?) >>> lp3944: 2009-06-19, Cameras, Lights, Indicators, Toys >>> pca955x: 2008-07-16, Cameras, Indicators (?) >>> >>> V4L2 API: >>> as3645a: 2011-05-05, Cameras >>> adp1653: 2011-05-05, Cameras >>> >>> V4L2 provides richest functionality, but there is often demand from >>> application developers to provide already established LED API. We would >>> like to have an unified user interface for flash devices. Some of devices >>> already have the LED API driver exposing limited set of a Flash IC >>> functionality. In order to support all required features the LED API >>> would have to be extended or the V4L2 API would need to be used. However >>> when switching from a LED to a V4L2 Flash driver existing LED API >>> interface would need to be retained. >>> >>> Proposed solution >>> >>> This patch adds V4L2 helper functions to register existing V4L2 flash >>> subdev as LED class device. After registration via v4l2_leddev_register >>> appropriate entry in /sys/class/leds/ is created. During registration all >>> V4L2 flash controls are enumerated and corresponding attributes are added. >>> >>> I have attached also patch with new max77693-led driver using v4l2_leddev. >>> This patch requires presence of the patch "max77693: added device tree >>> support": https://patchwork.kernel.org/patch/2414351/ . >>> >>> Additional features >>> >>> - simple API to access all V4L2 flash controls via sysfs, >>> - V4L2 subdevice should not be registered by V4L2 device to use it, >>> - LED triggers API can be used to control the device, >>> - LED device is optional - it will be created only if V4L2_LEDDEV >>> configuration option is enabled and the subdev driver calls >>> v4l2_leddev_register. >>> >>> Doubts >>> >>> This RFC is a result of a uncertainty which API developers should expose >>> by their flash drivers. It is a try to gluing together both APIs. I am not >>> sure if it is the best solution, but I hope there will be some discussion >>> and hopefully some decisions will be taken which way we should follow. >> The LED subsystem provides similar APIs for the Camera driver. >> With LED trigger event, flash and torch are enabled/disabled. >> I'm not sure this is applicable for you. >> Could you take a look at LED camera trigger feature? >> >> For the camera LED trigger, >> https://git.kernel.org/cgit/linux/kernel/git/cooloney/linux-leds.git/commit/ >> ?h=f or-next&id=48a1d032c954b9b06c3adbf35ef4735dd70ab757 >> >> Example of camera flash driver, >> https://git.kernel.org/cgit/linux/kernel/git/cooloney/linux-leds.git/commit/ >> ?h=f or-next&id=313bf0b1a0eaeaac17ea8c4b748f16e28fce8b7a > I think we should decide on one API. Implementing two APIs for a single device > is usually messy, and will result in different feature sets (and different > bugs) being implemented through each API, depending on the driver. > Interactions between the APIs are also a pain point on the kernel side to > properly synchronize calls. > > The LED API is too limited for torch and flash usage, but I'm definitely open > to moving flash devices to the LED API is we can extend it in a way that it > covers all the use cases. > Extending LED API IMHO seems to be quite straightforward - by adding attributes for supported functionalities. We just need a specification for standard flash/torch attributes. I could prepare an RFC about it if there is a will to explore this direction. -- Regards Andrzej Hajda <a.hajda@xxxxxxxxxxx> -- 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
