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

[Lukas Wunner]

On Wed, May 31, 2017 at 10:48:37AM +0200, Florian Echtler wrote:
> 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
> radeon.pcie_gen2=0
> [  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

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).

Another possible explanation would be that panel power needs to be
enabled by writing to the registers which control the pins mentioned
below.


> 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?

*shrug*  Unfortunately I'm not familiar at all with radeontool. :-(

Best regards,

Lukas