Bug#768157: machine hangs when loading cirrus with modeset=1 while booted with vga=791

[Ben Hutchings]

Control: tag -1 upstream confirmed

On Wed, 2014-11-05 at 15:02 +0100, Evgeni Golov wrote:
> Package: src:linux
> Version: 3.16.7-1
> Severity: normal
> 
> Hi,
> 
> while testing the new Grml release, I noticed an interesting hang of QEMU when
> the machine is booted. The initial testing was done using [1] in QEMU from Sid
> (2.1+dfsg-5), but I also could reproduce it with the same QEMU and a fresh
> Jessie install with both, 3.16.5-1 and 3.16.7-1.
> 
> To reproduce:
> * boot a fresh Jessie with 3.16 kernel in QEMU and vga=791 as bootparam
> * modprobe cirrus modeset=1
> * machine hangs
> 
> I am not sure this will happen on real cirrus HW, as I don't have any, but QEMU
> is quite widespread and cirrus is the default VGA driver.
[...]

The cirrus KMS driver only binds to QEMU Cirrus devices, not real
hardware.  It has been working for me, but I can reproduce the apparent
hang with the 'vga=791' parameter.

It's not actually hanging, though - using a serial console, I see the
error messages:

[    1.976874] [drm:cirrus_vram_init] *ERROR* can't reserve VRAM
[    1.978067] cirrus 0000:00:02.0: Fatal error during GPU init: -6

and I can log in there.  But, as the driver detects this error after the
point of no return (remove_conflicting_framebuffers()), the display
remains broken.

Ben.

-- 
Ben Hutchings
The program is absolutely right; therefore, the computer must be wrong.
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