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Message-ID: <20140814043925.GN16460@valkosipuli.retiisi.org.uk> Date: Thu, 14 Aug 2014 07:39:25 +0300 From: Sakari Ailus <sakari.ailus@....fi> To: Jacek Anaszewski <j.anaszewski@...sung.com>, Bryan Wu <cooloney@...il.com>, Richard Purdie <rpurdie@...ys.net> Cc: linux-leds@...r.kernel.org, devicetree@...r.kernel.org, linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, kyungmin.park@...sung.com, b.zolnierkie@...sung.com Subject: Re: [PATCH/RFC v4 06/21] leds: add API for setting torch brightness Bryan and Richard, Your opinion would be much appreciated to a question myself and Jacek were pondering. Please see below. On Thu, Aug 07, 2014 at 03:12:09PM +0200, Jacek Anaszewski wrote: > Hi Sakari, > > On 08/04/2014 02:50 PM, Sakari Ailus wrote: > >Hi Jacek, > > > >Thank you for your continued efforts on this! > > > >On Mon, Aug 04, 2014 at 02:35:26PM +0200, Jacek Anaszewski wrote: > >>On 07/16/2014 11:54 PM, Sakari Ailus wrote: > >>>Hi Jacek, > >>> > >>>Jacek Anaszewski wrote: > >>>... > >>>>diff --git a/include/linux/leds.h b/include/linux/leds.h > >>>>index 1a130cc..9bea9e6 100644 > >>>>--- a/include/linux/leds.h > >>>>+++ b/include/linux/leds.h > >>>>@@ -44,11 +44,21 @@ struct led_classdev { > >>>> #define LED_BLINK_ONESHOT_STOP (1 << 18) > >>>> #define LED_BLINK_INVERT (1 << 19) > >>>> #define LED_SYSFS_LOCK (1 << 20) > >>>>+#define LED_DEV_CAP_TORCH (1 << 21) > >>>> > >>>> /* Set LED brightness level */ > >>>> /* Must not sleep, use a workqueue if needed */ > >>>> void (*brightness_set)(struct led_classdev *led_cdev, > >>>> enum led_brightness brightness); > >>>>+ /* > >>>>+ * Set LED brightness immediately - it is required for flash led > >>>>+ * devices as they require setting torch brightness to have > >>>>immediate > >>>>+ * effect. brightness_set op cannot be used for this purpose because > >>>>+ * the led drivers schedule a work queue task in it to allow for > >>>>+ * being called from led-triggers, i.e. from the timer irq context. > >>>>+ */ > >>> > >>>Do we need to classify actual devices based on this? I think it's rather > >>>a different API behaviour between the LED and the V4L2 APIs. > >>> > >>>On devices that are slow to control, the behaviour should be asynchronous > >>>over the LED API and synchronous when accessed through the V4L2 API. How > >>>about implementing the work queue, as I have suggested, in the > >>>framework, so > >>>that individual drivers don't need to care about this and just implement > >>>the > >>>synchronous variant of this op? A flag could be added to distinguish > >>>devices > >>>that are fast so that the work queue isn't needed. > >>> > >>>It'd be nice to avoid individual drivers having to implement multiple > >>>ops to > >>>do the same thing, just for differing user space interfacs. > >>> > >> > >>It is not only the matter of a device controller speed. If a flash > >>device is to be made accessible from the LED subsystem, then it > >>should be also compatible with led-triggers. Some of led-triggers > >>call brightness_set op from the timer irq context and thus no > >>locking in the callback can occur. This requirement cannot be > >>met i.e. if i2c bus is to be used. This is probably the primary > >>reason for scheduling work queue tasks in brightness_set op. > >> > >>Having the above in mind, setting a brightness in a work queue > >>task must be possible for all LED Class Flash drivers, regardless > >>whether related devices have fast or slow controller. > >> > >>Let's recap the cost of possible solutions then: > >> > >>1) Moving the work queues to the LED framework > >> > >> - it would probably require extending led_set_brightness and > >> __led_set_brightness functions by a parameter indicating whether it > >> should call brightness_set op in the work queue task or directly; > >> - all existing triggers would have to be updated accordingly; > >> - work queues would have to be removed from all the LED drivers; > >> > >>2) adding led_set_torch_brightness API > >> > >> - no modifications in existing drivers and triggers would be required > >> - instead, only the modifications from the discussed patch would > >> be required > >> > >>Solution 1 looks cleaner but requires much more modifications. > > > >How about a combination of the two, i.e. option 1 with the old op remaining > >there for compatibility with the old drivers (with a comment telling it's > >deprecated)? > > > >This way new drivers will benefit from having to implement this just once, > >and modifications to the existing drivers could be left for later. > > It's OK for me, but the opinion from the LED side guys is needed here > as well. Ping. > >The downside is that any old drivers wouldn't get V4L2 flash API but that's > >entirely acceptable in my opinion since these would hardly be needed in use > >cases that would benefit from V4L2 flash API. > > In the version 4 of the patch set I changed the implementation, so that > a flash led driver must call led_classdev_flash_register to get > registered as a LED Flash Class device and v4l2_flash_init to get > V4L2 Flash API. In effect old drivers will have no chance to get V4L2 > Flash API either way. -- Kind regards, Sakari Ailus e-mail: sakari.ailus@....fi XMPP: sailus@...iisi.org.uk -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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