NanoPI M4 and HDCP

[ph1l1p139]

Hi,

 

I'm running Armbian Bionic 4.4 (Linux nanopim4 4.4.190-rk3399 #5 SMP Sun Sep 1 23:12:43 CEST 2019 aarch64 aarch64 aarch64 GNU/Linux) on a NanoPI M4 and I'm trying to enable HDCP on the HDMI output.

I can't figure out how to do this (or if it is even possible).

 

dmesg shows that the driver/hardware knows about HDCP to some extent

pi@nanopim4:~$ dmesg | grep -i hdcp
[    3.307777] dwhdmi-rockchip ff940000.hdmi: Detected HDMI TX controller v2.11a with HDCP (DWC HDMI 2.0 TX PHY)

 xrandr lists no content_protection property

pi@nanopim4:~$ xrandr --prop
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
HDMI-1 connected primary 1920x1080+0+0 1152mm x 648mm
        EDID:
                00ffffffffffff0010e3140211000082
                ff1c010380331d7806e295a2554f9f26
                115054ffff80d1c0b300950f950081c0
                81408180714f4dd000a0f0703e803020
                350080884200001e000000fd0a01ff01
                ff3c0000000000000000000000fc0044
                47433231340a20202020202000000010
                000000000000000000000000000001c1
                02033571230f1707836900004561605f
                5e5dee0f0000000000000000000000f0
                0168030c00ffff1078016ad85dc40178
                80010000004dd000a0f0703e80302035
                0080884200001eb46600a0f0701f8030
                20350080884200001e293680a070381f
                403020350040442100001eb71a80a070
                1c10203020350040442100009e0000ff
        hue: 50
                range: (0, 100)
        saturation: 50
                range: (0, 100)
        contrast: 50
                range: (0, 100)
        brightness: 50
                range: (0, 100)
        hdmi_quant_range: default
                supported: default, limit, full
        hdmi_output_mode_capacity: 7
                range: (0, 15)
        hdmi_color_depth_capacity: 19
                range: (0, 255)
        hdmi_output_colorimetry: None
                supported: None, ITU_2020
        hdmi_output_format: output_rgb
                supported: output_rgb, output_ycbcr444, output_ycbcr422, output_ycbcr420, output_ycbcr_high_subsampling, output_ycbcr_low_subsampling, invalid_output
        hdmi_output_depth: 24bit
                supported: Automatic, 24bit, 30bit

 

There is a sysfs node for content_protection created, but it doesn't return any values

pi@nanopim4:~$ cd /sys/class/drm/card0-HDMI-A-1/
pi@nanopim4:/sys/class/drm/card0-HDMI-A-1$ ls -lh
total 0
-r--r--r-- 1 root root 4.0K Oct  2 12:35 audioformat
-rw-r--r-- 1 root root 4.0K Oct  2 13:05 content_protection
lrwxrwxrwx 1 root root    0 Oct  2 12:35 device -> ../../card0
-r--r--r-- 1 root root 4.0K Oct  2 12:35 dpms
-r--r--r-- 1 root root    0 Oct  2 12:35 edid
-r--r--r-- 1 root root 4.0K Oct  2 12:35 enabled
-r--r--r-- 1 root root 4.0K Oct  2 12:35 mode
-r--r--r-- 1 root root 4.0K Oct  2 12:35 modes
drwxr-xr-x 2 root root    0 Oct  2 12:35 power
-rw-r--r-- 1 root root 4.0K Oct  2 12:35 status
lrwxrwxrwx 1 root root    0 Oct  2 12:35 subsystem -> ../../../../../../class/drm
-rw-r--r-- 1 root root 4.0K Oct  2 12:35 uevent
pi@nanopim4:/sys/class/drm/card0-HDMI-A-1$ cat content_protection
pi@nanopim4:/sys/class/drm/card0-HDMI-A-1$

Writing to it with the values that look like they should work (by inspecting drivers/gpu/drm/drm_crtc.c and drivers/gpu/drm/drm_sysfs.c) just returns Invalid Value:

pi@nanopim4:/sys/class/drm/card0-HDMI-A-1$ su
Password:
root@nanopim4:/sys/class/drm/card0-HDMI-A-1# echo "Desired" > content_protection
bash: echo: write error: Invalid argument

(I've also tried echo -n, and various capitalisations of: Undesired, Desired, Enabled. All of which have the same result).

Am I missing something here?

Is it possible to enable HDCP on the HDMI output?

 

Thanks,

Phil