Hi Jacek, On Fri, May 09, 2014 at 09:18:55AM +0200, Jacek Anaszewski wrote: > Hi Sakari, > > On 05/07/2014 09:58 AM, Sakari Ailus wrote: > >Hi Jacek, > > > >On Wed, May 07, 2014 at 09:20:17AM +0200, Jacek Anaszewski wrote: > >>On 05/06/2014 11:10 AM, Sakari Ailus wrote: > >>>Hi Jacek, > >>> > >>>On Tue, May 06, 2014 at 08:44:41AM +0200, Jacek Anaszewski wrote: > >>>>Hi Sakari, > >>>> > >>>>On 05/02/2014 01:06 PM, Sakari Ailus wrote: > >>>> > >>>>>>>>[...] > >>>>>>>>>>+static inline enum led_brightness v4l2_flash_intensity_to_led_brightness( > >>>>>>>>>>+ struct led_ctrl *config, > >>>>>>>>>>+ u32 intensity) > >>>>>>>>> > >>>>>>>>>Fits on a single line. > >>>>>>>>> > >>>>>>>>>>+{ > >>>>>>>>>>+ return intensity / config->step; > >>>>>>>>> > >>>>>>>>>Shouldn't you first decrement the minimum before the division? > >>>>>>>> > >>>>>>>>Brightness level 0 means that led is off. Let's consider following case: > >>>>>>>> > >>>>>>>>intensity - 15625 > >>>>>>>>config->step - 15625 > >>>>>>>>intensity / config->step = 1 (the lowest possible current level) > >>>>>>> > >>>>>>>In V4L2 controls the minimum is not off, and zero might not be a possible > >>>>>>>value since minimum isn't divisible by step. > >>>>>>> > >>>>>>>I wonder how to best take that into account. > >>>>>> > >>>>>>I've assumed that in MODE_TORCH a led is always on. Switching > >>>>>>the mode to MODE_FLASH or MODE_OFF turns the led off. > >>>>>>This way we avoid the problem with converting 0 uA value to > >>>>>>led_brightness, as available torch brightness levels start from > >>>>>>the minimum current level value and turning the led off is > >>>>>>accomplished on transition to MODE_OFF or MODE_FLASH, by > >>>>>>calling brightness_set op with led_brightness = 0. > >>>>> > >>>>>I'm not sure if we understood the issue the same way. My concern was that if > >>>>>the intensity isn't a multiple of step (but intensity - min is), the above > >>>>>formula won't return a valid result (unless I miss something). > >>>>> > >>>> > >>>>Please note that v4l2_flash_intensity_to_led_brightness is called only > >>>>from s_ctrl callback, and thus it expects to get the intensity aligned > >>>>to the step value, so it will always be a multiple of step. > >>>>Is it possible that s_ctrl callback would be passed a non-aligned > >>>>control value? > >>> > >>>In a nutshell: value - min is aligned but value is not. Please see > >>>validate_new() in drivers/media/v4l2-core/v4l2-ctrls.c . > >>> > >> > >>Still, to my mind, value is aligned. > >> > >>Below I execute the calculation steps one by one > >>according to the V4L2_CTRL_TYPE_INTEGER case in the > >>validate_new function: > >> > >>c->value = 35000 > >> > >>val = c->value + step / 2; // 35000 + 15625 / 2 = 42812 > >>val = clamp(val, min, max); // val = 42812 > >>offset = val - min; // 42812 - 15625 = 27187 > >>offset = step * (offset / step); // 15625 * (27187 / 15625) = 15625 > >>c->value = min + offset; // 15625 + 15625 = 31250 > >> > >>Value is aligned to the nearest step. > >> > >>Please spot any discrepancies in my way of thinking if there > >>are any :) > > > >min is aligned to step above. This is not necessarily the case. And if min > >is not aligned, neither is value. > > > > Thanks for spotting this. Below are improved versions of the conversion > functions. Please let me know if you have any comments. > > static inline > enum led_brightnessv4l2_flash_intensity_to_led_brightness( > struct led_ctrl *config, > u32 intensity) > { > return ((intensity - config->min) / config->step) + 1; > } > > static inline > u32 v4l2_flash_led_brightness_to_intensity( > struct led_ctrl *config, > enum led_brightness brightness) > { > return ((brightness - 1) * config->step) + config->min; V4L2 control integer values are signed, thus s32 instead of u32. Otherwise looks good to me. -- Regards, Sakari Ailus e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html