On Wed, Oct 16, 2013 at 4:54 PM, Bryan Wu cooloney@gmail.com wrote:
On Wed, Oct 16, 2013 at 4:36 PM, Milo Kim milo.kim@ti.com wrote:
Hi Bryan,
On 10/17/2013 02:17 AM, Bryan Wu wrote:
On Tue, Oct 15, 2013 at 6:49 PM, Milo Kim milo.kim@ti.com wrote:
Hi Bryan,
On 10/16/2013 03:37 AM, Bryan Wu wrote:
On Fri, Oct 11, 2013 at 12:38 AM, Laurent Pinchart laurent.pinchart@ideasonboard.com wrote:
Hi Bryan,
On Thursday 10 October 2013 17:02:18 Bryan Wu wrote: > > > On Mon, Oct 7, 2013 at 3:24 PM, Laurent Pinchart wrote: >> >> >> On Tuesday 08 October 2013 00:06:23 Sakari Ailus wrote: >>> >>> >>> On Tue, Sep 24, 2013 at 11:20:53AM +0200, Thierry Reding wrote: >>>> >>>> >>>> On Mon, Sep 23, 2013 at 10:27:06PM +0200, Sylwester Nawrocki wrote: >>>>> >>>>> >>>>> On 09/23/2013 06:37 PM, Oliver Schinagl wrote: >>>>>> >>>>>> >>>>>> On 09/23/13 16:45, Sylwester Nawrocki wrote: >>>>>>> >>>>>>> >>>>>>> Hi, >>>>>>> >>>>>>> I would like to have a short discussion on LED flash devices >>>>>>> support >>>>>>> in the kernel. Currently there are two APIs: the V4L2 and LED >>>>>>> class >>>>>>> API exposed by the kernel, which I believe is not good from user >>>>>>> space POV. Generic applications will need to implement both >>>>>>> APIs. >>>>>>> I >>>>>>> think we should decide whether to extend the led class API to >>>>>>> add >>>>>>> support for more advanced LED controllers there or continue to >>>>>>> use >>>>>>> the both APIs with overlapping functionality. There has been >>>>>>> some >>>>>>> discussion about this on the ML, but without any consensus >>>>>>> reached >>>>>>> [1]. >>>>>> >>>>>> >>>>>> >>>>>> What about the linux-pwm framework and its support for the >>>>>> backlight >>>>>> via dts? >>>>>> >>>>>> Or am I talking way to uninformed here. Copying backlight to >>>>>> flashlight with some minor modification sounds sensible in a >>>>>> way... >>>>> >>>>> >>>>> >>>>> I'd assume we don't need yet another user interface for the LEDs >>>>> ;) >>>>> AFAICS the PWM subsystem exposes pretty much raw interface in >>>>> sysfs. >>>>> The PWM LED controllers are already handled in the leds-class API, >>>>> there is the leds_pwm driver (drivers/leds/leds-pwm.c). >>>>> >>>>> I'm adding linux-pwm and linux-leds maintainers at Cc so someone >>>>> may >>>>> correct me if I got anything wrong. >>>> >>>> >>>> >>>> The PWM subsystem is most definitely not a good fit for this. The >>>> only >>>> thing it provides is a way for other drivers to access a PWM device >>>> and >>>> use it for some specific purpose (pwm-backlight, leds-pwm). >>>> >>>> The sysfs support is a convenience for people that needs to use a >>>> PWM >>>> in a way for which no driver framework exists, or for which it >>>> doesn't >>>> make sense to write a driver. Or for testing. >>>> >>>>> Presumably, what we need is a few enhancements to support in a >>>>> standard way devices like MAX77693, LM3560 or MAX8997. There is >>>>> already a led class driver for the MAX8997 LED controller >>>>> (drivers/leds/leds-max8997.c), but it uses some device-specific >>>>> sysfs >>>>> attributes. >>>>> >>>>> Thus similar devices are currently being handled by different >>>>> subsystems. The split between the V4L2 Flash and the leds class >>>>> API >>>>> WRT to Flash LED controller drivers is included in RFC [1], it >>>>> seems >>>>> still up to date. >>>>> >>>>>>> [1] http://www.spinics.net/lists/linux-leds/msg00899.html >>>> >>>> >>>> >>>> Perhaps it would make sense for V4L2 to be able to use a LED as >>>> exposed >>>> by the LED subsystem and wrap it so that it can be integrated with >>>> V4L2? If functionality is missing from the LED subsystem I suppose >>>> that >>>> could be added. >>> >>> >>> >>> The V4L2 flash API supports also xenon flashes, not only LED ones. >>> That >>> said, I agree there's a common subset of functionality most LED >>> flash >>> controllers implement. >>> >>>> If I understand correctly, the V4L2 subsystem uses LEDs as flashes >>>> for >>>> camera devices. I can easily imagine that there are devices out >>>> there >>>> which provide functionality beyond what a regular LED will provide. >>>> So >>>> perhaps for things such as mobile phones, which typically use a >>>> plain >>>> LED to illuminate the surroundings, an LED wrapped into something >>>> that >>>> emulates the flash functionality could work. But I doubt that the >>>> LED >>>> subsystem is a good fit for anything beyond that. >>> >>> >>> >>> I originally thought one way to do this could be to make it as easy >>> as >>> possible to support both APIs in driver which some aregued, to which >>> I >>> agree, is rather poor desing. >>> >>> Does the LED API have a user space interface library like libv4l2? >>> If >>> yes, one option oculd be to implement the wrapper between the V4L2 >>> and >>> LED APIs there so that the applications using the LED API could also >>> access those devices that implement the V4L2 flash API. Torch mode >>> functionality is common between the two right now AFAIU, >>> >>> The V4L2 flash API also provides a way to strobe the flash using an >>> external trigger which typically connected to the sensor (and the >>> user >>> can choose between that and software strobe). I guess that and Xenon >>> flashes aren't currently covered by the LED API. >> >> >> >> The issue is that we have a LED API targetted at controlling LEDs, a >> V4L2 >> flash API targetted at controlling flashes, and hardware devices >> somewhere >> in the middle that can be used to provide LED or flash function. >> Merging >> the two APIs on the kernel side, with a compatibility layer for both >> kernel space and user space APIs, might be an idea worth >> investigating. > > > > I'm so sorry for jumping in the discussion so late. Some how the > emails from linux-media was archived in my Gmail and I haven't > checkout this for several weeks. > > I agree right now LED API doesn't quite fit for the usage of V4L2 > Flash API. But I'd also like to see a unified API. > > Currently, LED API are exported to user space as sysfs interface, > while V4L2 Flash APIs are like IOCTL and user space library. We also > merged some LED Flash trigger into LED subsystem. My basic idea is > what about creating or expanding the LED Flash trigger driver and > provide a well defined sysfs interface, which can be wrapped into user > space libv4l2.
The biggest reason why we're not fond of sysfs-based APIs for media devices is that they can't provide atomicity. There's no way to set multiple parameters in a single operation.
We can't get rid of the sysfs LEDs API, but maybe we could have a unified kernel LED/flash subsystem that would provide both a sysfs-based API to ensure compatibility with current userspace software and an ioctl-based API (possibly through V4L2 controls). That way LED/flash devices would be registered with a single subsystem, and the corresponding drivers won't have to care about the API exposed to userspace. That would require a major refactoring of the in- kernel APIs though.
I agree this. I'm thinking about expanding the ledtrig-camera.c created by Milo Kim. This trigger will provide flashing and strobing control of a LED device and for sure the LED device driver like drivers/leds/leds-lm355x.c.
So we basically can do this:
- add V4L2 Flash subdev into ledtrig-camera.c. So this trigger driver
can provide trigger API to kernel drivers as well as V4L2 Flash API to userspace. 2. add the real flash torch functions into LED device driver like leds-lm355x.c, this driver will still provide sysfs interface and extended flash/torch control sysfs interface as well.
I'm not sure about whether we need some change in V4L2 internally. But actually Andrzej Hajda's patchset is quite straightforward, but we just need put those V4L2 Flash API into a LED trigger driver and the real flash/torch operation in a LED device driver.
Milo, could you please give some comments here?
General LED trigger APIs were created not for the application interface but for any kernel space driver. The LED camera trigger APIs are used by a camera driver, not application.
That's basically correct, but trigger sometime can also provide sysfs interface which might be used by user space app.
Actually this camera flash/torch trigger API can also be used by V4L2 Flash subdev. We create a V4L2 Flash subdev in the driver, which will expose V4L2 API to user space. And this V4L2 Flash subdev will use this flash/torch trigger API to talk with our LED core and it really doesn't need to know the details about the LED flash/torch chip, if we can provide a good interface between trigger and LED device driver.
So benefits are a) one trigger/V4L2 Flash subdev driver can be used by multiple LED chips b) LED chip driver just need to provide standard or extended LED API to support flash/torch c) LED chip driver still keep those LED sysfs interface to user space and won't break user space application
Some LED devices provide basic LED functionalities and high current features like a flash and a torch.(eg. LM3554, LM3642) The reason why I added the LED camera trigger is "for providing multiple operations(LEDs, flash and torch) by one LED device driver".
For example, A LED indicator is controlled via the LED sysfs. And flash and torch are controlled by a camera driver - calls exported LED trigger function, ledtrig_flash_ctrl().
My understanding is the V4L2 subsystem provides rich IOCTLs for the media device. I agree that the V4L2 is more proper interface for camera *application*.
So, my suggestion is:
- If a device has only flash/torch functionalities, then register the
driver as the V4L2 sub-device.
- If a device provides not only flash/torch but also LED features,
then create the driver as the MFD.
We really don't need to separate them, one LED device driver can provide flash/torch/normal functions in on driver. I think LED device driver is trying to provide the LED chip's hardware functions, like flash/torch/indicator etc. how to use it, we can choose different trigger. That gives us the maxim flexibility.
For example, LM3555 (and AS3645A) is used only for the camera. Then, this driver is registered as the V4L2 sub-device. (drivers/media/i2c/as3645a.c) - no change at all.
That's current solution, we plan to unify this two API since those chip are basically LED.
On the other hands, LM3642 has an indicator mode with flash/torch. Then, it will consist of 3 parts - MFD core, LED(indicator) and V4L2(flash/torch).
So if one LED device driver can support that, we don't need these 3 parts.
Let me clarify our discussion briefly.
For the flash and torch, there are scattered user-space APIs. We need to unify them.
We are considering supporting V4L2 structures in the LED camera trigger. Then, camera application controls the flash/torch via not the LED sysfs but the V4L2 ioctl interface. So, changing point is the ledtrig-camera.c. No chip driver changes at all.
Yeah, my proposal is to add V4L2 interface into ledtrig-camera.c. For existing chip driver like yours LM3555, I guess we don't need to big change but for future support for new chip or adding flash/torch to existing chip, we need to create or change chip driver. Because eventually those flash/torch/indicator operation happens in chip driver.
Thanks, -Bryan
Remove my old email address.
-Bryan