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

[Florian Echtler]

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).
>>
> The ATI card has MXM_PNL_PWR_EN and MXM_PNL_BL_EN pins.  Those must be
> enabled for the panel to light up.  Perhaps radeon needs to be extended
> to do that.  One theory is that this is done via ACPI, but perhaps
> only if a certain operating system is running.  Dump the ACPI tables
> and search DSDT and SSDT* tables for methods relating to the ATI card
> and/or backlight.  If you find checks for OSDW there (e.g. in _PS0,
> i.e. on resume), it means the AML code is only executed on Darwin.
I've already had a look at the ACPI tables; there seem to be no references to
the "official" backlight/display control functions (no _BL? or _DO? methods).

> Conversely !OSDW means the code is only executed on Windows (Boot Camp).
> Linux masquerades as Darwin, but this can be disabled with
> acpi_osi=!Darwin on the command line.  It's worth trying if that changes
> the behaviour.  If it does, then macOS likely sets those pins on resume
> and we need to do the same in radeon.
There are OSDW checks present, however, booting with acpi_osi=!Darwin doesn't
make a difference to the backlight behaviour.

I'd be grateful for other suggestions...

Best regards, Florian
-- 
SENT FROM MY DEC VT50 TERMINAL


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