DDC communication failed (Operation not supported) over HDMI

[tao-song-tfs]

Hi,

 We use yocto with iMX8 and I added ddcutil to the yocto build. I tried to use it to adjust the brightness of the display.  I got an error when I ran ddcutil detect:

root@imx8mp-var-dart:~# ddcutil detect
Invalid display
I2C bus:  /dev/i2c-6
EDID synopsis:
   Mfg id:               MST
   Model:                MStar Demo
   Product code:         48
   Serial number:
   Binary serial number: 1 (0x00000001)
   Manufacture year:     2010,  Week: 10
DDC communication failed

I found a similar issue "DDC communication failed over HDMI #148" but I got a different error message  "Operation not supported" when I ran ddcutil interrogate command. Please see the attached file.

Could you give some suggestion of how to resolve the issue?

Thanks!

 Regards,

 Tom

ddcutil interrogate output.txt

[rockowitz]

Looking at file drivers/gpu/drm/bridge/synopsys/dw-hdmi.c in the Linux 6.2.9 source, I see the following at line 443 in function dw_hdmi_i2c_xfer():

 443     if (addr == DDC_CI_ADDR)
 444         /*
 445          * The internal I2C controller does not support the multi-byte
 446          * read and write operations needed for DDC/CI.
 447          * TOFIX: Blacklist the DDC/CI address until we filter out
 448          * unsupported I2C operations.
 449          */
 450         return -EOPNOTSUPP;
 451 

So it would appear that the Designware HDMI driver does not support DDC.

This very old google hit suggests that there was as some point work to enable DDC support.

I suggest you follow up with the folks responsible for the Designware HDMI driver. If you find out anything more, please post that information here so that others can benefit.

[tao-song-tfs]

Hi,

 Thanks for looking into this issue. Sorry I didn't get notice when the issue was updated.

 I will give it a try as you suggested and update the issue if I can find a solution.

 Thanks for help!

 Regards,

 Tom