Jetson TX2/r28 Display debug

Get prepared
This section focuses on debug display driver issue on rel-28.x BSP. Drivers of tegra display controller are under kernel source: https://developer.nvidia.com/embedded/downloads For T210(TX1) kernel/display/drivers/video/tegra/dc/ For T186(TX2). Note that TX2 still uses driver code of T210. kernel/t18x/drivers/video/tegra/dc

Tips
dmesg |grep tegradc sudo cat /sys/kernel/debug/tegradc.X/mode #X=0,1,2. sudo cat /sys/class/graphics/fb0/mode #if more than one fb, just change the fbX to whatever you want. sudo cat /sys/kernel/debug/tegradc.X/edid #X=0,1,2. 1. Prepare a known 256byte EDID. 2. set use_fallback = true; in tegra_edid_get_monspecs under edid.c. 3. fill in the known EDID to default_720p_edid[256]. sudo cat /sys/kernel/debug/tegradc.0/stats underflows: 35 underflows_a: 143 underflows_b: 0 underflows_c: 0
 * Print out display kernel related message
 * Print current mode in dc
 * Print current mode in fbcon
 * Capture edid
 * Forcing edid
 * Do I hit underflow? (red screen or blank line flicker)

sudo echo 4 > /sys/class/graphics/fb0/blank  #blank display and power down sudo echo 1 > /sys/class/graphics/fb0/blank  #blank display and show the background color sudo echo 0 > /sys/class/graphics/fb0/blank  #unblank display
 * Blank/Unblank window/display

Issues

 * HDMI
 * Display is not be able to up. Moreover, system is not able to up.(Fixed after rel-28.2)
 * https://devtalk.nvidia.com/default/topic/1003956/jetson-tx2/tx2-not-booting-up-with-hdmi-connected/post/5160211/#5160211
 * X11 returns below error and cause failure (TX2)
 * https://devtalk.nvidia.com/default/topic/1027467
 * This is due to uart1_tx pin. Please review the OEM design guide for your carrier board