V4L/DVB (8870): gspca: Fix dark room problem with sonixb.

When using the sonixb driver in a dark room and given that the autoexposure
algorithm starts with a setting most suitable for daylight, the picture
produced by the cam may actually be 100% black leading to a avg_lum value of 0,
so an avg_lum value of 0 does not always signal an exposure settings change
(which it normally does). This patch adds a check for the really black image
case and stops dropping all frames as invalid in this case.

Signed-off-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/media/video/gspca/sonixb.c b/drivers/media/video/gspca/sonixb.c
index bde9ea9b980e..64bc758fbae5 100644
--- a/drivers/media/video/gspca/sonixb.c
+++ b/drivers/media/video/gspca/sonixb.c
@@ -52,6 +52,7 @@ MODULE_LICENSE("GPL");
 struct sd {
         struct gspca_dev gspca_dev;     /* !! must be the first item */
         atomic_t avg_lum;
+        int prev_avg_lum;
 
         unsigned char gain;
         unsigned char exposure;
@@ -1022,10 +1023,19 @@ static void sd_pkt_scan(struct gspca_dev *gspca_dev,
                                 } else {
                                         lum = data[i + 8] + (data[i + 9] << 8);
                                 }
-                                if (lum == 0) {
+                                /* When exposure changes midway a frame we
+                                   get a lum of 0 in this case drop 2 frames
+                                   as the frames directly after an exposure
+                                   change have an unstable image. Sometimes lum
+                                   *really* is 0 (cam used in low light with
+                                   low exposure setting), so do not drop frames
+                                   if the previous lum was 0 too. */
+                                if (lum == 0 && sd->prev_avg_lum != 0) {
                                         lum = -1;
                                         sd->frames_to_drop = 2;
-                                }
+                                        sd->prev_avg_lum = 0;
+                                } else
+                                        sd->prev_avg_lum = lum;
                                 atomic_set(&sd->avg_lum, lum);
 
                                 if (sd->frames_to_drop) {