LeMaker Guitar:Configure HDMI resolution

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The newer display structure has been integrated into the system image with v1601 version, which support the resolution self-adaption of HDMI and HDMI as master display device and so on. The document mainly describes how to configure the resolution of HDMI based on it. If you are using the system image with v1511 version or older, suggest you update system image to v1601 version or newer.

Resolution self-adaption of HDMI

The newer system image support resolution self-adaption of HDMI according to the EDID information getted from uboot stage.
You should plugin the HDMI device before start Guitar, and can enable/disable this function by editing the DTS file of uboot(lemaker_guitar.dts), like this:

  hdmi: hdmi@b02c0000{
                status="okay";
                hdcp_onoff = <0>;
                channel_invert = <0>;
                bit_invert = <0>;
                hotplugable = <0>;
                bootable = <0>; 
                bootrotate = <0>;
                default_resolution = "auto";
        };

disable the edid function at uboot stage when the bootable=<0>; enable the edid function at uboot stage when the bootable=<1>
Noted that this will also disable display of the "LeMaker" LOGO at uboot stage, and not all the display device and HDMI to VGA cable support the EDID, you can judge it via the uboot log information:

parse hdmi edid information successfully
In:    serial
Out:   serial
Err:   serial
Net:   owl_mac

If you get the EDID sucessfully, you will see "successfully", otherwise you will get "unsuccessfuly".

Manually set the resolution of HDMI

We can manually set the resolution of HDMI when the self-adaption of HDMI failed.
Firstly, view the supported resolutions of the HDMI when the HDMI as the master device:

# cat /sys/class/graphics/fb0/modes
U:1920x1080p-60
U:720x576p-50
U:1280x720p-50
D:720x480p-59
D:1280x720p-60
D:1920x1080p-60

Secondly, Set the resolution by editing the /etc/rc.local file, add this line to the file:

echo "D:1280x720p-60" >/sys/class/graphics/fb0/modes

Finally, reboot the system.

NOTE: If the self-adaption of HDMI is failed, the output of HDMI will be 720P.