drivers/media/usb/gspca/autogain_functions.c

Source file repositories/reference/linux-study-clean/drivers/media/usb/gspca/autogain_functions.c

File Facts

System
Linux kernel
Corpus path
drivers/media/usb/gspca/autogain_functions.c
Extension
.c
Size
5009 bytes
Lines
166
Domain
Driver Families
Bucket
drivers/media
Inferred role
Driver Families: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

if (avg_lum > desired_avg_lum) {
			if (gain > gain_knee)
				gain--;
			else if (exposure > exposure_knee)
				exposure--;
			else if (gain > gspca_dev->gain->default_value)
				gain--;
			else if (exposure > gspca_dev->exposure->minimum)
				exposure--;
			else if (gain > gspca_dev->gain->minimum)
				gain--;
			else
				break;
		} else {
			if (gain < gspca_dev->gain->default_value)
				gain++;
			else if (exposure < exposure_knee)
				exposure++;
			else if (gain < gain_knee)
				gain++;
			else if (exposure < gspca_dev->exposure->maximum)
				exposure++;
			else if (gain < gspca_dev->gain->maximum)
				gain++;
			else
				break;
		}
	}

	if (gain != orig_gain) {
		v4l2_ctrl_s_ctrl(gspca_dev->gain, gain);
		retval = 1;
	}
	if (exposure != orig_exposure) {
		v4l2_ctrl_s_ctrl(gspca_dev->exposure, exposure);
		retval = 1;
	}

	if (retval)
		gspca_dbg(gspca_dev, D_FRAM, "autogain: changed gain: %d, expo: %d\n",
			  gain, exposure);
	return retval;
}
EXPORT_SYMBOL(gspca_expo_autogain);

/* Autogain + exposure algorithm for cameras with a coarse exposure control
   (usually this means we can only control the clockdiv to change exposure)
   As changing the clockdiv so that the fps drops from 30 to 15 fps for
   example, will lead to a huge exposure change (it effectively doubles),
   this algorithm normally tries to only adjust the gain (between 40 and
   80 %) and if that does not help, only then changes exposure. This leads
   to a much more stable image then using the knee algorithm which at
   certain points of the knee graph will only try to adjust exposure,
   which leads to oscillating as one exposure step is huge.

   Returns 0 if no changes were made, 1 if the gain and or exposure settings
   where changed. */
int gspca_coarse_grained_expo_autogain(
			struct gspca_dev *gspca_dev,
			int avg_lum,
			int desired_avg_lum,
			int deadzone)
{
	s32 gain_low, gain_high, gain, orig_gain, exposure, orig_exposure;
	int steps, retval = 0;

	if (v4l2_ctrl_g_ctrl(gspca_dev->autogain) == 0)
		return 0;

	orig_gain = gain = v4l2_ctrl_g_ctrl(gspca_dev->gain);
	orig_exposure = exposure = v4l2_ctrl_g_ctrl(gspca_dev->exposure);

	gain_low  = (s32)(gspca_dev->gain->maximum - gspca_dev->gain->minimum) /
		    5 * 2 + gspca_dev->gain->minimum;
	gain_high = (s32)(gspca_dev->gain->maximum - gspca_dev->gain->minimum) /
		    5 * 4 + gspca_dev->gain->minimum;

	/* If we are of a multiple of deadzone, do multiple steps to reach the
	   desired lumination fast (with the risc of a slight overshoot) */
	steps = (desired_avg_lum - avg_lum) / deadzone;

	gspca_dbg(gspca_dev, D_FRAM, "autogain: lum: %d, desired: %d, steps: %d\n",
		  avg_lum, desired_avg_lum, steps);

	if ((gain + steps) > gain_high &&
	    exposure < gspca_dev->exposure->maximum) {
		gain = gain_high;
		gspca_dev->exp_too_low_cnt++;
		gspca_dev->exp_too_high_cnt = 0;
	} else if ((gain + steps) < gain_low &&

Annotation

Implementation Notes