Target Display Mode: send_byte(0x52, 0x0300) fail: 0x40

[Doofus100500]

iMac 27-Inch, late 2012 (iMac13,2)
Hi, everything was build without errors, using original cable. But after booting i see only command prompt.

sudo /usr/bin/tdm_toggle
Target Display Mode : send_byte(0x52, 0x0300) fail: 0x40
MVHR: read arg fail

read_smc get_key_type error

enabled, toggling OFF ...
Target Display Mode : send_byte(0x52, 0x0300) fail: 0x40
MVHR: read arg fail

read_smc get_key_type error

send_byte(0x52, 0x0300) fail: 0x40
MVHR: read arg fail

read_smc get_key_type error

disabled.

[gpdm]

Known issue, this was as well reported in upstream project, see floe/smc_util#2

I have currently no solution to this particular error.

[Bellavene]

Unfortunately, 2012 iMacs are using Thunderbolt instead of miniDP, that's why it doesn't work. And TDM on Thunderbolt macs is working only with Thunderbolt macs, M series macs are out of luck too.

[dbarrington]

I also tried this, and the same for me unfortunately. I am happy to test/debug/provide output if anyone wants to look further at this issue.

[DJMoffinz]

Unfortunately, 2012 iMacs are using Thunderbolt instead of miniDP, that's why it doesn't work. And TDM on Thunderbolt macs is working only with Thunderbolt macs, M series macs are out of luck too.

I have this issue on a mac of that era, but i've got it connected using a thunderbolt 2 cable (with a t2->t3 adapter from apple) to my linux laptop which supports thunderbolt 3 input.

given that it works from mac to mac, could it be that there needs to be some software on my laptop as well as the mac to get this working?

oh, i also have a slightly different error:

Target Display Mode : send_byte(0x52, 0x0300) fail: 0x40
MVHR: read arg fail

read_smc get_key_type error

enabled.

it says enabled instead of disabled. Then it says Please press enter to activate this console. and does the same thing every time i do.

[Doofus100500]

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