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 :)
Regards,
Jacek Anaszewski
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