[media] gspca: New file autogain_functions.h

This file contains functions for the auto gain.
It must be used with the new control mechanism.

Acked-by: Hans de Goede <[e-mail]>
Signed-off-by: Jean-François Moine <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/video/gspca/autogain_functions.h

···
+/*
+ * Functions for auto gain.
+ *
+ * Copyright (C) 2010-2011 Hans de Goede <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+/* auto gain and exposure algorithm based on the knee algorithm described here:
+   http://ytse.tricolour.net/docs/LowLightOptimization.html
+
+   Returns 0 if no changes were made, 1 if the gain and or exposure settings
+   where changed. */
+static inline int auto_gain_n_exposure(
+			struct gspca_dev *gspca_dev,
+			int avg_lum,
+			int desired_avg_lum,
+			int deadzone,
+			int gain_knee,
+			int exposure_knee)
+{
+	struct sd *sd = (struct sd *) gspca_dev;
+	int i, steps, gain, orig_gain, exposure, orig_exposure;
+	int retval = 0;
+
+	orig_gain = gain = sd->ctrls[GAIN].val;
+	orig_exposure = exposure = sd->ctrls[EXPOSURE].val;
+
+	/* 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 = abs(desired_avg_lum - avg_lum) / deadzone;
+
+	PDEBUG(D_FRAM, "autogain: lum: %d, desired: %d, steps: %d",
+		avg_lum, desired_avg_lum, steps);
+
+	for (i = 0; i < steps; i++) {
+		if (avg_lum > desired_avg_lum) {
+			if (gain > gain_knee)
+				gain--;
+			else if (exposure > exposure_knee)
+				exposure--;
+			else if (gain > sd->ctrls[GAIN].def)
+				gain--;
+			else if (exposure > sd->ctrls[EXPOSURE].min)
+				exposure--;
+			else if (gain > sd->ctrls[GAIN].min)
+				gain--;
+			else
+				break;
+		} else {
+			if (gain < sd->ctrls[GAIN].def)
+				gain++;
+			else if (exposure < exposure_knee)
+				exposure++;
+			else if (gain < gain_knee)
+				gain++;
+			else if (exposure < sd->ctrls[EXPOSURE].max)
+				exposure++;
+			else if (gain < sd->ctrls[GAIN].max)
+				gain++;
+			else
+				break;
+		}
+	}
+
+	if (gain != orig_gain) {
+		sd->ctrls[GAIN].val = gain;
+		setgain(gspca_dev);
+		retval = 1;
+	}
+	if (exposure != orig_exposure) {
+		sd->ctrls[EXPOSURE].val = exposure;
+		setexposure(gspca_dev);
+		retval = 1;
+	}
+
+	if (retval)
+		PDEBUG(D_FRAM, "autogain: changed gain: %d, expo: %d",
+			gain, exposure);
+	return retval;
+}
+
+/* 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 oscilating as one exposure step is huge.
+
+   Note this assumes that the sd struct for the cam in question has
+   exp_too_high_cnt and exp_too_high_cnt int members for use by this function.
+
+   Returns 0 if no changes were made, 1 if the gain and or exposure settings
+   where changed. */
+static inline int coarse_grained_expo_autogain(
+			struct gspca_dev *gspca_dev,
+			int avg_lum,
+			int desired_avg_lum,
+			int deadzone)
+{
+	struct sd *sd = (struct sd *) gspca_dev;
+	int steps, gain, orig_gain, exposure, orig_exposure;
+	int gain_low, gain_high;
+	int retval = 0;
+
+	orig_gain = gain = sd->ctrls[GAIN].val;
+	orig_exposure = exposure = sd->ctrls[EXPOSURE].val;
+
+	gain_low = (sd->ctrls[GAIN].max - sd->ctrls[GAIN].min) / 5 * 2;
+	gain_low += sd->ctrls[GAIN].min;
+	gain_high = (sd->ctrls[GAIN].max - sd->ctrls[GAIN].min) / 5 * 4;
+	gain_high += sd->ctrls[GAIN].min;
+
+	/* 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;
+
+	PDEBUG(D_FRAM, "autogain: lum: %d, desired: %d, steps: %d",
+		avg_lum, desired_avg_lum, steps);
+
+	if ((gain + steps) > gain_high &&
+	    exposure < sd->ctrls[EXPOSURE].max) {
+		gain = gain_high;
+		sd->exp_too_low_cnt++;
+		sd->exp_too_high_cnt = 0;
+	} else if ((gain + steps) < gain_low &&
+		   exposure > sd->ctrls[EXPOSURE].min) {
+		gain = gain_low;
+		sd->exp_too_high_cnt++;
+		sd->exp_too_low_cnt = 0;
+	} else {
+		gain += steps;
+		if (gain > sd->ctrls[GAIN].max)
+			gain = sd->ctrls[GAIN].max;
+		else if (gain < sd->ctrls[GAIN].min)
+			gain = sd->ctrls[GAIN].min;
+		sd->exp_too_high_cnt = 0;
+		sd->exp_too_low_cnt = 0;
+	}
+
+	if (sd->exp_too_high_cnt > 3) {
+		exposure--;
+		sd->exp_too_high_cnt = 0;
+	} else if (sd->exp_too_low_cnt > 3) {
+		exposure++;
+		sd->exp_too_low_cnt = 0;
+	}
+
+	if (gain != orig_gain) {
+		sd->ctrls[GAIN].val = gain;
+		setgain(gspca_dev);
+		retval = 1;
+	}
+	if (exposure != orig_exposure) {
+		sd->ctrls[EXPOSURE].val = exposure;
+		setexposure(gspca_dev);
+		retval = 1;
+	}
+
+	if (retval)
+		PDEBUG(D_FRAM, "autogain: changed gain: %d, expo: %d",
+			gain, exposure);
+	return retval;
+}