media: atomisp: Add testing instructions to TODO file

Testing the atomisp can be a bit tricky. The BYT/CHT CPUs are not
very powerful so some apps like camorama cannot run at full FPS.

Add instructions for how to test with gstreamer which does
runs at full FPS without issues.

Link: https://lore.kernel.org/r/20230604161406.69369-6-hdegoede@redhat.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/staging/media/atomisp/TODO

@@ -78,3 +78,36 @@ TODO
   the firmware files
 
 * The atomisp code still has a lot of cruft which needs cleaning up
+
+
+Testing
+=======
+
+Since libcamera support is not available yet, the easiest way to test for
+now is using v4l2-ctl to select the input and gstreamer for streaming.
+
+To select the input run:
+
+v4l2-ctl -i <input>
+
+Where <input> is 0 (front cam) or 1 (back cam).
+
+The simplest gstreamer pipeline for testing running the sensor
+at its max resolution is:
+
+gst-launch-1.0 v4l2src ! videoconvert ! xvimagesink sync=false
+
+To select e.g 640x480 as resolution use:
+
+gst-launch-1.0 v4l2src ! video/x-raw,format=YV12,width=640,height=480 ! \
+               videoconvert ! xvimagesink sync=false
+
+And to show fps use:
+
+gst-launch-1.0 v4l2src ! video/x-raw,format=YV12,width=640,height=480 ! \
+               videoconvert ! fpsdisplaysink video-sink=xvimagesink sync=false
+
+Often the image will be over / under exposed. This can be fixed by using
+v4l2-ctl on the sensor subdev to tweak the exposure ctrl; or by using a GUI
+app for v4l2-controls which also supports subdev such as the Fedora patched
+gtk-v4l tool.