[media] gspca_pac7311: Properly set the compression balance

Before this patch sometimes the camera would run out of bandwidth when
running at 640x480@30.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 25 insertions, 5 deletions

diff --git a/drivers/media/video/gspca/pac7311.c b/drivers/media/video/gspca/pac7311.c
index 54b4ab68f0b5..5ccf0b41ffc5 100644
--- a/drivers/media/video/gspca/pac7311.c
+++ b/drivers/media/video/gspca/pac7311.c
@@ -29,7 +29,18 @@
  * 0x1b         Auto white balance related, bit 0 is AWB enable (inverted)
  *              bits 345 seem to toggle per color gains on/off (inverted)
  * 0x78         Global control, bit 6 controls the LED (inverted)
- * 0x80         JPEG compression ratio ? Best not touched
+ * 0x80         Compression balance, interesting settings:
+ *              0x01 Use this to allow the camera to switch to higher compr.
+ *                   on the fly. Needed to stay within bandwidth @ 640x480@30
+ *              0x1c From usb captures under Windows for 640x480
+ *              0x2a Values >= this switch the camera to a lower compression,
+ *                   using the same table for both luminance and chrominance.
+ *                   This gives a sharper picture. Usable only at 640x480@ <
+ *                   15 fps or 320x240 / 160x120. Note currently the driver
+ *                   does not use this as the quality gain is small and the
+ *                   generated JPG-s are only understood by v4l-utils >= 0.8.9
+ *              0x3f From usb captures under Windows for 320x240
+ *              0x69 From usb captures under Windows for 160x120
  *
  * Register page 4:
  *
@@ -408,12 +419,21 @@ static void setexposure(struct gspca_dev *gspca_dev)
          *  640x480 mode and page 4 reg 2 <= 3 then it must be 9
          */
         reg_w(gspca_dev, 0xff, 0x01);
-        if (gspca_dev->cam.cam_mode[(int)gspca_dev->curr_mode].priv &&
-                        sd->ctrls[EXPOSURE].val <= 3) {
+        if (gspca_dev->width != 640 && sd->ctrls[EXPOSURE].val <= 3)
                 reg_w(gspca_dev, 0x08, 0x09);
-        } else {
+        else
                 reg_w(gspca_dev, 0x08, 0x08);
-        }
+
+        /*
+         * Page1 register 80 sets the compression balance, normally we
+         * want / use 0x1c, but for 640x480@30fps we must allow the
+         * camera to use higher compression or we may run out of
+         * bandwidth.
+         */
+        if (gspca_dev->width == 640 && sd->ctrls[EXPOSURE].val == 2)
+                reg_w(gspca_dev, 0x80, 0x01);
+        else
+                reg_w(gspca_dev, 0x80, 0x1c);
 
         /* load registers to sensor (Bit 0, auto clear) */
         reg_w(gspca_dev, 0x11, 0x01);