if HDMI display is connected then execute setenv vidargs ‘mxc_hdmi.only_cea=1 video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24 video=mxcfb1:off video=mxcfb2:off video=mxcfb3:off fbmem=32M’
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To set the vidargs depending on whether an LVDS or HDMI display is connected at startup on your i.MX6 module, you can use a script in U-Boot to detect the display type and set the appropriate environment variables. Here’s a step-by-step guide:
Modify U-Boot Script:
Create a U-Boot script that checks for the presence of an HDMI display and sets the vidargs accordingly. If HDMI is not detected, it defaults to LVDS.
Detect HDMI Display:
Use the i2c command in U-Boot to check for the presence of an HDMI display. HDMI displays typically have an EDID EEPROM that can be read over I2C.
Set Environment Variables:
Based on the detection, set the vidargs environment variable.
Here is an example U-Boot script:
# Check for HDMI display by reading EDID over I2C
i2c dev 2
i2c probe 0x50
if test $? -eq 0; then
# HDMI display detected
setenv vidargs 'mxc_hdmi.only_cea=1 video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24 video=mxcfb1:off video=mxcfb2:off video=mxcfb3:off fbmem=32M'
else
# Default to LVDS display
setenv vidargs 'video=mxcfb0:dev=ldb,if=RGB24 fbmem=32M'
fi
# Save the environment variables
saveenv
Integrate Script into U-Boot:
You can integrate this script into your U-Boot environment by adding it to the boot command sequence. For example, you can add it to the bootcmd environment variable:
setenv bootcmd 'run detect_display; run boot_sequence'
setenv detect_display 'i2c dev 2; i2c probe 0x50; if test $? -eq 0; then setenv vidargs "mxc_hdmi.only_cea=1 video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24 video=mxcfb1:off video=mxcfb2:off video=mxcfb3
While the approach suggested by @ToradexAI is not absurd and could work for some use cases, I don’t believe it will work for the Apalis iMX6.
What you could do is check the status of the HDMI_IH_PHY_STAT0 register.
When the system boots without HDMI connected it should be 0, otherwise it should be different from 0.
Here is an example of running this on u-boot:
setexpr.b hdmistat *120104
if test "${hdmistat}" = "00"; then echo "HDMI was not connected"; else echo "HDMI was connected"; fi
i have tested it out and it works. I am wondering from where this memory address *120104 comes from. Can we put general purpose register. I am asking if upgrade the version of U-boot, this may fail.
Through i2c I tried to detect the HDMI bus and in the kernel space I see the bus 3 is connected to HDMI
root@apalis-imx6:~# i2cdetect 2
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-2.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- UU -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- UU -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
root@apalis-imx6:~# i2cdetect 1
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-1.
I will probe address range 0x03-0x77.
Continue? [Y/n] ^[[Ay
Aborting on user request.
root@apalis-imx6:~# i2cdetect 1
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-1.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
root@apalis-imx6:~# i2cdetect 0
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-0.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- UU UU -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
root@apalis-imx6:~# i2cdetect 3
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-3.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- 38 -- 3a 3b -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: UU -- -- -- 54 -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
But in the U-boot space, there is no bus 3
Apalis iMX6 # i2c dev 3
Setting bus to 3
Failure changing bus number (-19)
Apalis iMX6 # i2c dev 1
Setting bus to 1
Apalis iMX6 # i2c probe
Valid chip addresses: 00 08 41 78
Apalis iMX6 # i2c dev 0
Setting bus to 0
Apalis iMX6 # i2c probe
Valid chip addresses: 21 22
Apalis iMX6 # i2c dev 2
Setting bus to 2
Apalis iMX6 # i2c probe
Valid chip addresses:
Apalis iMX6 # i2c dev 3
Setting bus to 3
Failure changing bus number (-19)
Apalis iMX6 # i2c probe
Valid chip addresses:
This is the address of the PHY Interface Interrupt Status Register (HDMI_IH_PHY_STAT0).
Therefore it should not change even if u-boot is updated.
You can check more information about it in the i.MX6Q/D Reference Manual (Requires Login).
