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

Florian Echtler floe at
Wed May 31 08:48:37 UTC 2017

On 30.05.2017 12:54, Lukas Wunner wrote:
> On Tue, May 30, 2017 at 11:34:17AM +0200, Florian Echtler wrote:
>> On 26.05.2017 23:03, Lukas Wunner wrote:
>>> On Fri, May 26, 2017 at 02:13:29PM +0200, Florian Echtler wrote:
>>>> I'm running Ubuntu 16.04.2 on a 27" unibody iMac 10,1 from 2009. However, even
>>>> with the most recent HWE stack (kernel 4.8), the display stays black after
>>>> suspend. I can ssh into the machine, so wakeup is OK, but the display is
>>>> entirely black (backlight stays off).
> So, just to confirm, if you never plug in an external DP source and the iMac
> comes out of sleep, the display stays black?

Correct, verified this just now.

> If you log in via ssh and look at dmesg, was radeon able to train the DP
> link again?  No error messages, nothing?

Here are the relevant dmesg lines after wakeup:

[  157.622950] [drm] enabling PCIE gen 2 link speeds, disable with
[  157.626077] [drm] PCIE GART of 1024M enabled (table at 0x000000000014C000).
[  157.626094] radeon 0000:02:00.0: WB enabled
[  157.626097] radeon 0000:02:00.0: fence driver on ring 0 use gpu addr
0x0000000010000c00 and cpu addr 0xffffa1242dfd6c00
[  157.626098] radeon 0000:02:00.0: fence driver on ring 3 use gpu addr
0x0000000010000c0c and cpu addr 0xffffa1242dfd6c0c
[  157.626315] radeon 0000:02:00.0: fence driver on ring 5 use gpu addr
0x000000000005c598 and cpu addr 0xffffbc3081c1c598
[  157.672183] [drm] ring test on 0 succeeded in 1 usecs
[  157.672187] [drm] ring test on 3 succeeded in 2 usecs
[  157.847098] [drm] ring test on 5 succeeded in 1 usecs
[  157.847102] [drm] UVD initialized successfully.
[  157.847121] [drm] ib test on ring 0 succeeded in 0 usecs
[  157.847136] [drm] ib test on ring 3 succeeded in 0 usecs
[  158.524061] [drm] ib test on ring 5 succeeded

And this is logged in Xorg.0.log after wakeup:

[   229.956] (II) RADEON(0): Allocate new frame buffer 320x200 stride 384
[   229.956] (II) RADEON(0): VRAM usage limit set to 219596K

xrandr still shows the eDP output as connected and active with 2560x1440 resolution.

> Is the panel off or is it on but merely with 0% brightness?

The backlight is definitely off. I've tried to shine a torch onto the panel and
see if any content is visible, but it looks like the panel itself is off, too.

> There's a block of pins on the GPU for "system management" which contains
> a bunch of GPIO, OEM and reserved pins.  Three of these are used to control
> the panel when it's switched to the radeon card:
> pin 23	   PNL_PWR_EN
> pin 25	   PNL_BL_EN
> pin 27	   PNL_BL_PWM
> Basically you'd need to know what these are set to before and after sleep.
> I don't know how to access them, presumably via a BAR register.  A quick
> look at the RV730-specific registers in drivers/gpu/drm/radeon/*.h did not
> yield anything useful, but someone at AMD may be able to find this out.

Can I perhaps use radeontool for this? I.e. dump registers before and after
sleep and see if there's a difference? Or is radeontool too old to know about
the correct registers?

Best, Florian

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