On 2020-06-10 18:23, n952162 wrote:
> On 2020-06-10 13:48, n952162 wrote:
>> On 2020-06-09 23:53, n952162 wrote:
>>> I posted about this problem perhaps a year ago - when running with
>>> AMDGPU, my system won't turn off, I have to hold the power button down
>>> for a long time, forcing it down.
>>>
>>> At that time, various people commented. but AMDGPU didn't work at all
>>> for me in the end, didn't talk to my HDMI display.
>>>
>>> I gave up on it.
>>>
>>> Thanks to all the great help here, I finally got my system properly
>>> updated and AMDGPU working, and it  finally talks to my HDMI display.
>>> But, it still doesn't shut down.
>>>
>>> Is it a bug?  Is my system still not right?  Is there something I have
>>> to do yet?
>>>
>>>
>>
>> The following assignment is on the linux line when booting in grub:
>>
>> amdgpu.dc=1
>>
>> When I make that 0, the system shuts down properly when the power button
>> is pressed.
>>
>> When it's 1, the system hangs after blank screen  when that button is
>> pressed.
>>
>>
>>
>
> I found this in the AMDGPU webpage:
>
>     /AMDGPU with Display Core was first implemented for VEGA10
>     (GCN5.0) and RAVEN (with DCN 1.0) GPUs/APUs. Kernels before
>     version 4.17 have (experimental) DC support for older cards
>     (GCN1.1 and newer) via command line option /amdgpu.dc=1/, which
>     may work better than the older radeon kernel module. Likewise, if
>     DC needs to be disabled for any particular reason, option
>     /amdgpu.dc=0/can be used on the kernel command line.
>     /
>
> It's not clear to me if  DC serves a function in kernels >= 4.17 or
> why it's installed as default by grub ...
>
> I don't see anything similar in the new kernel parameters I posted to
> this topic, but I do find this in my .config file:
>
> #
> # Display Engine Configuration
> #
> CONFIG_DRM_AMD_DC=y
> CONFIG_DRM_AMD_DC_DCN1_0=y
> # CONFIG_DEBUG_KERNEL_DC is not set
>
> Was this left over from an earlier configuration and not properly
> cleaned out, or is it necessary, for some reason?
>
> Can someone explain how the amdgpu.dc=1 parameter gets passed to grub?
>
>

Okay, I found out how amdgpu.dc=1 gets into grub - via
/etc/default/grub.  I'm not sure who put it there - was it the kernel
make process?

Note that even with amdgpu.dc=0, I still have (finally!) HDMI output to
my monitor.  There's a lot of talk on the internet about whether
amdgpu.dc=1 is good or bad, but nobody seems to know or explain what
it's about, or the role of Display Core WRT to AMDGPU.

The only important thing unresolved for me now is whether I still need
those DRM_AMD_DC kernel variables, above.