Hi

Am 28.07.22 um 13:13 schrieb Michael Ellerman:
> Thomas Zimmermann <tzimmermann@suse.de> writes:
>> (was: drm: Add driverof PowerPC OF displays)
>>
>> PowerPC's Open Firmware offers a simple display buffer for graphics
>> output. Add ofdrm, a DRM driver for the device. As with the existing
>> simpledrm driver, the graphics hardware is pre-initialized by the
>> firmware. The driver only provides blitting, no actual DRM modesetting
>> is possible.
> 
> Hi Thomas,
> 
> I tried to test this on a 32-bit ppc Mac Mini but didn't have much luck.

Awesome! Thanks for testing.

> But I'm probably doing something wrong because I'm a graphics noob.
> 
> The machine normally uses CONFIG_DRM_RADEON, so I turned that off, and
> turned DRM_OFDRM on.

It needs

CONFIG_DRM=y
CONFIG_OFDRM=y
CONFIG_FB=y
CONFIG_DRM_FBDEV_EMULATION=y

plus some dependencies, but menuconfig should select them automatically. 
I've attached my config for ppc64le, which has the correct DRM and FB 
options.

> 
> When I boot I get boot messages but only one screen worth, the messages
> don't scroll at all, which is unusual. But I'm not sure if that's
> related to ofdrm or something else.
> 
> The machine does come up, I can login via SSH. Is there some way to
> start X to exercise the driver from an SSH login?

For ofdrm, X needs a patch that isn't there yet. It's a trivial change 
along the lines of [1], but still missing. So X is probably not worth 
trying yet.

But at least the framebuffer console should work.

I suspect that it's an issue with the framebuffer's color mode, which 
might not be supported yet. Could you please fetch the output from dmesg 
after the machine booted?

Best regards
Thomas

[1] 
https://gitlab.freedesktop.org/xorg/xserver/-/commit/b9218fadf3c09d83566549279d68886d8258f79c

> 
> cheers

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev