Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color

[Mathieu Malaterre <malat@debian.org>]

On Mon, May 30, 2016 at 9:50 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
> Control: reassign src:linux 4.5.4-1
> Control: tag -1 help
>
> On Mon, 2016-05-30 at 18:42 +0200, Mathieu Malaterre wrote:
>> Package: linux-image-4.5.0-2-powerpc
>> Version: 4.5.4-1
>>
>> During Debian installation the background color is inverted on PPC system.
>> At least on my Mac Mini G4, the default background color shows up as red
>> from begining to start (only the last screen turn blue).
>>
>> Looking at the module loaded during the installation I can see radeonfb,
>> which I suspect is the one responsible for handling of `/dev/fb0`.
>>
>> After installation I tried reproducing this color inversion without any
>> luck so far.
>>
>> It is non-trivial to `rmmod radeon`, so instead I used (and rebooted):
>>
>> $ cat /etc/modprobe.d/radeon.conf
>> blacklist radeon
>>
>> However upon reboot `/dev/fb0` is already setup.
>
> Of course, because there is no character-based display mode on Power
> Macs (in general).
>
>> But neither radeonfb nor
>> radeon module seems to be loaded (using lsmod) but lspci output is rather
>> confusing [*].
>
> lspci lists all kernel modules that match a particular PCI device's ID,
> and separately whether any kernel driver is currently bound to the
> device.
>
>> I can also see:
>>
>> $ cat /proc/fb
>> 0 OFfb ATY,RockHo
>
> As I would expect, the generic Open Firmware framebuffer driver is
> behind /dev/fb0.  If a hardware-specific driver is loaded, that will
> take over from it.

Thank you ! Ok now I understand. d-i tried to modprobe `radeonfb` but
fails since framebuffer is already taken by Open Firmare, as can be
seen in the dmesg log:

[   96.551486] radeonfb 0000:00:10.0: enabling device (0006 -> 0007)
[   96.551526] radeonfb 0000:00:10.0: BAR 0: can't reserve [mem
0x98000000-0x9fffffff pref]
[   96.551531] radeonfb (0000:00:10.0): cannot request region 0.
[   96.551545] radeonfb: probe of 0000:00:10.0 failed with error -16

One way to double check if color inversion happen using `radeonfb` is
simply to type at boot: command line:

install32 nomodeset video=offb:off

(instead of the default `install32`).

At least I know where too look now. Maybe the palette is setup
backward for powerpc.