Messages in this thread | | | Date | Fri, 09 May 2014 09:18:55 +0200 | From | Jacek Anaszewski <> | Subject | Re: [PATCH/RFC v3 5/5] media: Add registration helpers for V4L2 flash sub-devices |
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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; }
Regards, Jacek Anaszewski
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