[media] gspca - main: Change the bandwidth estimation of isochronous transfer

Having:
- a mean image size of 0.375 time the max compressed image size and
- a frame rate of 30 fps for small images or with USB 2.0/3.0
seems more realistic and gives less image freezes.

Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/drivers/media/video/gspca/gspca.c b/drivers/media/video/gspca/gspca.c
index 5ce3557bde89..cdd43ff4aa02 100644
--- a/drivers/media/video/gspca/gspca.c
+++ b/drivers/media/video/gspca/gspca.c
@@ -633,13 +633,14 @@ static u32 which_bandwidth(struct gspca_dev *gspca_dev)
         u32 bandwidth;
         int i;
 
+        /* get the (max) image size */
         i = gspca_dev->curr_mode;
         bandwidth = gspca_dev->cam.cam_mode[i].sizeimage;
 
-        /* if the image is compressed, estimate the mean image size */
+        /* if the image is compressed, estimate its mean size */
         if (bandwidth < gspca_dev->cam.cam_mode[i].width *
                                 gspca_dev->cam.cam_mode[i].height)
-                bandwidth /= 3;
+                bandwidth = bandwidth * 3 / 8;  /* 0.375 */
 
         /* estimate the frame rate */
         if (gspca_dev->sd_desc->get_streamparm) {
@@ -649,7 +650,14 @@ static u32 which_bandwidth(struct gspca_dev *gspca_dev)
                 gspca_dev->sd_desc->get_streamparm(gspca_dev, &parm);
                 bandwidth *= parm.parm.capture.timeperframe.denominator;
         } else {
-                bandwidth *= 15;                /* 15 fps */
+
+                /* don't hope more than 15 fps with USB 1.1 and
+                 * image resolution >= 640x480 */
+                if (gspca_dev->width >= 640
+                 && gspca_dev->dev->speed == USB_SPEED_FULL)
+                        bandwidth *= 15;                /* 15 fps */
+                else
+                        bandwidth *= 30;                /* 30 fps */
         }
 
         PDEBUG(D_STREAM, "min bandwidth: %d", bandwidth);