[media] gspca - sn9c20x: Add automatic JPEG compression mechanism

The JPEG compression may be adjusted from the packet fill ratio and from
the flag 'USB FIFO full' returned in each frame.
The code is adapted from the one in gspca sonixj and uses a workqueue.

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

drivers/media/video/gspca/sn9c20x.c

···
 
 	struct gspca_ctrl ctrls[NCTRLS];
 
+	struct work_struct work;
+	struct workqueue_struct *work_thread;
+
+	u32 pktsz;			/* (used by pkt_scan) */
+	u16 npkt;
+	s8 nchg;
 	u8 fmt;				/* (used for JPEG QTAB update */
 
 #define MIN_AVG_LUM 80
···
 
 	u8 flags;
 };
+
+static void qual_upd(struct work_struct *work);
 
 struct i2c_reg_u8 {
 	u8 reg;
···
 
 	gspca_dev->cam.ctrls = sd->ctrls;
 
+	INIT_WORK(&sd->work, qual_upd);
 
 	return 0;
 }
···
 
 	reg_r(gspca_dev, 0x1061, 1);
 	reg_w1(gspca_dev, 0x1061, gspca_dev->usb_buf[0] | 0x02);
+
+	/* if JPEG, prepare the compression quality update */
+	if (mode & MODE_JPEG) {
+		sd->pktsz = sd->npkt = 0;
+		sd->nchg = 0;
+		sd->work_thread =
+			create_singlethread_workqueue(KBUILD_MODNAME);
+	}
+
 	return gspca_dev->usb_err;
 }
 
···
 
 	reg_r(gspca_dev, 0x1061, 1);
 	reg_w1(gspca_dev, 0x1061, gspca_dev->usb_buf[0] & ~0x02);
+}
+
+/* called on streamoff with alt==0 and on disconnect */
+/* the usb_lock is held at entry - restore on exit */
+static void sd_stop0(struct gspca_dev *gspca_dev)
+{
+	struct sd *sd = (struct sd *) gspca_dev;
+
+	if (sd->work_thread != NULL) {
+		mutex_unlock(&gspca_dev->usb_lock);
+		destroy_workqueue(sd->work_thread);
+		mutex_lock(&gspca_dev->usb_lock);
+		sd->work_thread = NULL;
+	}
 }
 
 static void do_autoexposure(struct gspca_dev *gspca_dev, u16 avg_lum)
···
 		do_autoexposure(gspca_dev, avg_lum);
 }
 
+/* JPEG quality update */
+/* This function is executed from a work queue. */
+static void qual_upd(struct work_struct *work)
+{
+	struct sd *sd = container_of(work, struct sd, work);
+	struct gspca_dev *gspca_dev = &sd->gspca_dev;
+
+	mutex_lock(&gspca_dev->usb_lock);
+	PDEBUG(D_STREAM, "qual_upd %d%%", sd->ctrls[QUALITY].val);
+	set_quality(gspca_dev);
+	mutex_unlock(&gspca_dev->usb_lock);
+}
+
 #if defined(CONFIG_INPUT) || defined(CONFIG_INPUT_MODULE)
 static int sd_int_pkt_scan(struct gspca_dev *gspca_dev,
 			u8 *data,		/* interrupt packet */
···
 	return ret;
 }
 #endif
+
+/* check the JPEG compression */
+static void transfer_check(struct gspca_dev *gspca_dev,
+			u8 *data)
+{
+	struct sd *sd = (struct sd *) gspca_dev;
+	int new_qual, r;
+
+	new_qual = 0;
+
+	/* if USB error, discard the frame and decrease the quality */
+	if (data[6] & 0x08) {				/* USB FIFO full */
+		gspca_dev->last_packet_type = DISCARD_PACKET;
+		new_qual = -5;
+	} else {
+
+		/* else, compute the filling rate and a new JPEG quality */
+		r = (sd->pktsz * 100) /
+			(sd->npkt *
+				gspca_dev->urb[0]->iso_frame_desc[0].length);
+		if (r >= 85)
+			new_qual = -3;
+		else if (r < 75)
+			new_qual = 2;
+	}
+	if (new_qual != 0) {
+		sd->nchg += new_qual;
+		if (sd->nchg < -6 || sd->nchg >= 12) {
+			sd->nchg = 0;
+			new_qual += sd->ctrls[QUALITY].val;
+			if (new_qual < QUALITY_MIN)
+				new_qual = QUALITY_MIN;
+			else if (new_qual > QUALITY_MAX)
+				new_qual = QUALITY_MAX;
+			if (new_qual != sd->ctrls[QUALITY].val) {
+				sd->ctrls[QUALITY].val = new_qual;
+				queue_work(sd->work_thread, &sd->work);
+			}
+		}
+	} else {
+		sd->nchg = 0;
+	}
+	sd->pktsz = sd->npkt = 0;
+}
 
 static void sd_pkt_scan(struct gspca_dev *gspca_dev,
 			u8 *data,			/* isoc packet */
···
 			    (data[33] << 10);
 		avg_lum >>= 9;
 		atomic_set(&sd->avg_lum, avg_lum);
+
+		if (gspca_dev->cam.cam_mode[(int) gspca_dev->curr_mode].priv
+				& MODE_JPEG)
+			transfer_check(gspca_dev, data);
+
 		gspca_frame_add(gspca_dev, LAST_PACKET, NULL, 0);
 		len -= 64;
 		if (len == 0)
···
 				data, len);
 		}
 	} else {
+		/* if JPEG, count the packets and their size */
+		if (gspca_dev->cam.cam_mode[(int) gspca_dev->curr_mode].priv
+				& MODE_JPEG) {
+			sd->npkt++;
+			sd->pktsz += len;
+		}
 		gspca_frame_add(gspca_dev, INTER_PACKET, data, len);
 	}
 }
···
 	.isoc_init = sd_isoc_init,
 	.start = sd_start,
 	.stopN = sd_stopN,
+	.stop0 = sd_stop0,
 	.pkt_scan = sd_pkt_scan,
 #if defined(CONFIG_INPUT) || defined(CONFIG_INPUT_MODULE)
 	.int_pkt_scan = sd_int_pkt_scan,