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

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On Tue, 2016-05-31 at 17:34 +0200, Mathieu Malaterre wrote:
> 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:
[...]

That's *not* what I thought was happening.  I was expecting radeonfb to
do something like this (in the radeon DRM driver):
https://sources.debian.net/src/linux/4.5.4-1/drivers/gpu/drm/radeon/radeon_drv.c/?hl=336#L336
and maybe to query offb about the existing framebuffer properties first.

So the problem is simpler: offb gets the palette or pixel format wrong
and loading radeonfb afterwards doesn't help because it doesn't take
over from offb.

On the installed system, the radeon driver is auto-loaded (although it
will still fail initialisation if the firmware is missing, except for
old ATI chips).  It can take over from offb and (presumably) gets the
colours right.

Ben.

-- 
Ben Hutchings
Any sufficiently advanced bug is indistinguishable from a feature.

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Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Mathieu Malaterre <malat@debian.org> - 2016-05-30 18:50 +0200
  Bug#825840: Acknowledgement (linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color) Mathieu Malaterre <malat@debian.org> - 2016-05-30 19:00 +0200
    Bug#825840: Acknowledgement (linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color) Mathieu Malaterre <malat@debian.org> - 2016-05-30 19:10 +0200
      Bug#825840: Acknowledgement (linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color) Ben Hutchings <ben@decadent.org.uk> - 2016-05-30 22:10 +0200
  Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Ben Hutchings <ben@decadent.org.uk> - 2016-05-30 22:00 +0200
    Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Geert Stappers <stappers@stappers.nl> - 2016-05-31 07:30 +0200
      Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Ben Hutchings <ben@decadent.org.uk> - 2016-05-31 13:00 +0200
        Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Milan Kupcevic <milan@debian.org> - 2016-05-31 20:20 +0200
      Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color "Lennart Sorensen" <lsorense@csclub.uwaterloo.ca> - 2016-05-31 15:20 +0200
    Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Mathieu Malaterre <malat@debian.org> - 2016-05-31 17:40 +0200
      Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Geert Stappers <stappers@stappers.nl> - 2016-05-31 18:20 +0200
      Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Ben Hutchings <ben@decadent.org.uk> - 2016-05-31 18:30 +0200
        Bug#825840: linux-image-4.5.0-2-powerpc: radeonfb display inverted red and blue color Mathieu Malaterre <malat@debian.org> - 2016-05-31 18:40 +0200

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