iMac 10,1 with Ubuntu 16.04: black screen after suspend

[Alex Deucher]

On Thu, Jun 1, 2017 at 4:27 AM, Florian Echtler <floe at butterbrot.org> wrote:
> On 31.05.2017 14:57, Alex Deucher wrote:
>> On Wed, May 31, 2017 at 5:21 AM, Lukas Wunner <lukas at wunner.de> wrote:
>>> On Wed, May 31, 2017 at 10:48:37AM +0200, Florian Echtler wrote:
>>>
>>> Hm, try booting with drm.debug=0xf to see if link training for the
>>> eDP connector succeeds.  If the link cannot be trained, it would
>>> explain that the screen stays black.  Should this indeed be the
>>> case, one possible explanation would be that the panel is muxed
>>> to the external port on resume and an appropriate command needs to
>>> be sent to the SMC to switch the mux to the radeon card.  This could
>>> be done in the ->resume_early hook of your APP000C platform driver.
>>> The apple-gmux driver contains something similar to power the discrete
>>> GPU down if it was off before suspend (because the BIOS always powers
>>> it up on resume).
>
> Here's the (substantial) dmesg output, with drm.debug=0xf:
> http://floe.butterbrot.org/external/radeon/dmesg_after_suspend
>
> I haven't been able to find any references to link training, though.

I need your dmesg from boot to confirm the display topology, but eDP
with r7xx asics was pretty rare.  I suspect your system just uses
LVDS; as such there is no link training involved.

Alex

>
>>> *shrug*  Unfortunately I'm not familiar at all with radeontool. :-(
>>
>> You can use the radeonreg tool to dump the display registers:
>> https://cgit.freedesktop.org/~agd5f/radeontool/
>> radeonreg regs dce3
>> replace dce3 with whatever dce version your card has.
>
> AFAICT the RV730 indeed has dce3, so I created a register dump before and after
> suspend:
> http://floe.butterbrot.org/external/radeon/regs_before_suspend.txt
> http://floe.butterbrot.org/external/radeon/regs_after_suspend.txt
>
> The diff, however, is quite large, I have no idea which registers to look for.
>
> Best, Florian
> --
> SENT FROM MY DEC VT50 TERMINAL
>