On Tue, May 21, 2013 at 3:54 AM, Sakari Ailus <sakari.ailus@xxxxxx> wrote: > Hi Andrzej, > > On Tue, May 21, 2013 at 10:34:53AM +0200, Andrzej Hajda wrote: >> On 12.05.2013 23:12, Sakari Ailus wrote: >> > On Wed, May 08, 2013 at 09:32:17AM +0200, Andrzej Hajda wrote: >> >> 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. >> > I don't like having two APIs either. Especially we shouldn't have multiple >> > drivers implementing different APIs for the same device. >> > >> > That said, I wonder if it's possible to support camera-related use cases >> > using the LED API: it's originally designed for quite different devices. >> > Even if you could handle flash strobing using the LED API, the functionality >> > provided by the Media controller and subdev APIs will always be missing: >> > device enumeration and association with the right camera. >> Is there a generic way to associate flash and camera subdevs in >> current V4L2 API? The only ways I see now are: >> - both belongs to the same media controller, but this is not enough if there >> is more than one camera subdev in that controller, > > Yes, there is. That's the group_id field in struct media_entity_desc. The > lens subdev is associated to the rest of the devices the same way. > >> - using media links/pads - at first sight it seems to be overkill/abuse... > > No. Links describe the flow of data, not relations between entities. > > ... > >> >>> 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. >> > I'm leaning towards providing a wrapper that provides torch functionality >> > using V4L2 flash API unless it's really proven to be insane. ;-) The code >> > supporting that in an individual flash driver should be minimal --- which is >> > what the patchset essentially already does. >> Providing only torch functionality do not require adding new attributes >> (besides the ones already present in the led_classdev), so the patch will >> be much simpler. > > Yes. Attributes could be added later on to the LED API to support flash and > the wrapper could be extended accordingly. My thinking is however that the > main use case is torch, not strobing flash, so it would be fulfilled already > without extensions to the LED API. > Sorry for replying so late. I think Milo Kim did some work in our LED subsystem by add LED Flash trigger for camera device. I agree it doesn't satisfy the usage of V4L2 Flash API and what I'm thinking about is expanding the LED Flash trigger driver to export a well defined sysfs interface, so user space libv4l2 can wrap it for applications. Thanks, -Bryan -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
