This subsystem handles DisplayPort video and audio output on the ZynqMP. It supports in-memory framebuffers with the DisplayPort DMA controller (xilinx-dpdma), as well as "live" video and audio from the programmable logic (PL). This subsystem can perform several transformations, including color space conversion, alpha blending, and audio mixing, although not all features are currently supported.
To support debugging and compliance testing, several test modes can be enabled though debugfs. The following files in /sys/kernel/debug/dri/X/DP-1/test/ control the DisplayPort test modes:
- active:
- Writing a 1 to this file will activate test mode, and writing a 0 will deactivate test mode. Writing a 1 or 0 when the test mode is already active/inactive will re-activate/re-deactivate test mode. When test mode is inactive, changes made to other files will have no (immediate) effect, although the settings will be saved for when test mode is activated. When test mode is active, changes made to other files will apply immediately.
- custom:
- Custom test pattern value
- downspread:
- Enable/disable clock downspreading (spread-spectrum clocking) by writing 1/0
- enhanced:
- Enable/disable enhanced framing
- ignore_aux_errors:
- Ignore AUX errors when set to 1. Writes to this file take effect immediately (regardless of whether test mode is active) and affect all AUX transfers.
- ignore_hpd:
- Ignore hotplug events (such as cable removals or monitor link retraining requests) when set to 1. Writes to this file take effect immediately (regardless of whether test mode is active).
- laneX_preemphasis:
- Preemphasis from 0 (lowest) to 2 (highest) for lane X
- laneX_swing:
- Voltage swing from 0 (lowest) to 3 (highest) for lane X
- lanes:
- Number of lanes to use (1, 2, or 4)
- pattern:
Test pattern. May be one of:
- video
- Use regular video input
- symbol-error
- Symbol error measurement pattern
- prbs7
- Output of the PRBS7 (x^7 + x^6 + 1) polynomial
- 80bit-custom
- A custom 80-bit pattern
- cp2520
- HBR2 compliance eye pattern
- tps1
- Link training symbol pattern TPS1 (/D10.2/)
- tps2
- Link training symbol pattern TPS2
- tps3
- Link training symbol pattern TPS3 (for HBR2)
- rate:
Rate in hertz. One of
- 5400000000 (HBR2)
- 2700000000 (HBR)
- 1620000000 (RBR)
You can dump the displayport test settings with the following command:
for prop in /sys/kernel/debug/dri/1/DP-1/test/*; do
printf '%-17s ' ${prop##*/}
if [ ${prop##*/} = custom ]; then
hexdump -C $prop | head -1
else
cat $prop
fi
done
The output could look something like:
active 1 custom 00000000 00 00 00 00 00 00 00 00 00 00 |..........| downspread 0 enhanced 1 ignore_aux_errors 1 ignore_hpd 1 lane0_preemphasis 0 lane0_swing 3 lane1_preemphasis 0 lane1_swing 3 lanes 2 pattern prbs7 rate 1620000000
The recommended test procedure is to connect the board to a monitor, configure test mode, activate test mode, and then disconnect the cable and connect it to your test equipment of choice. For example, one sequence of commands could be:
echo 1 > /sys/kernel/debug/dri/1/DP-1/test/enhanced echo tps1 > /sys/kernel/debug/dri/1/DP-1/test/pattern echo 1620000000 > /sys/kernel/debug/dri/1/DP-1/test/rate echo 1 > /sys/kernel/debug/dri/1/DP-1/test/ignore_aux_errors echo 1 > /sys/kernel/debug/dri/1/DP-1/test/ignore_hpd echo 1 > /sys/kernel/debug/dri/1/DP-1/test/active
at which point the cable could be disconnected from the monitor.
.. kernel-doc:: drivers/gpu/drm/xlnx/zynqmp_disp.h
.. kernel-doc:: drivers/gpu/drm/xlnx/zynqmp_dpsub.h
.. kernel-doc:: drivers/gpu/drm/xlnx/zynqmp_kms.h
.. kernel-doc:: drivers/gpu/drm/xlnx/zynqmp_disp.c
.. kernel-doc:: drivers/gpu/drm/xlnx/zynqmp_dp.c
.. kernel-doc:: drivers/gpu/drm/xlnx/zynqmp_kms.c