Merge pull request raspberrypi#270 from Gadgetoid/patch-3

Update display troubleshooting

Author: bennuttall

hardware/display/troubleshooting.md

@@ -28,6 +28,24 @@ sudo reboot
 * Make sure you've updated Raspbian, see above for steps.
 * Check the smaller ribbon cable is seated properly
 
+If you want to make sure your Pi has detected your touchscreen, try running:
+
+```bash
+dmesg | grep -i ft5406
+```
+
+You should see a couple of lines that look like this:
+
+```text
+[ 5.224267] rpi-ft5406 rpi_ft5406: Probing device
+[ 5.225960] input: FT5406 memory based driver as /devices/virtual/input/input3
+```
+
+A detected touchscreen will also cause the `fbheight` and `fbwidth` parameters in `/proc/cmdline` to equal 480 and 800 respectively ( the resolution of the screen ), you can verify this by running:
+
+```
+cat /proc/cmdline | grep bcm2708_fb
+```
 
 ### My screen is upside-down!