radeon RV730 in iMac troubleshooting

[Josh Moyer <JMoyer%nodomain.net@localhost>]

Hi Tech-Kern,
Sadly, the radeon DRM2 driver must be disabled with userconf in order to successfully boot a mid 2010 21.5" iMac (Radeon HD 4670 256MB/RV730) -- otherwise the screen goes black when the kernel is switching to userland/init.  I'm using 10_RC1 and also had this problem in the beta and also in 9, I think.

I hacked kern/init_main.c to panic on line 739 before the display goes dark and the last two dmesgs are:

pci_mem_find: void region (dev/pci/pci_map.c)
radeon0: map 5 failed (could not find corresponding source file)

Oddly, ddb isn't invoked, despite ddb.onpanic=1, so I can't generate a kernel memory dump.

I tried getting more debug output by using various config options, including the following without much luck: DIAGNOSTIC, DEBUG, DRM_DEBUG, DRM2_DEBUG, RADEON_DEBUG

I even tried to comment out radeon and uncomment radeondrm in the config, but get a lot of errors at link time complaining about undefined references in the radeondrm code.

Before I start hacking at pci_map.c, I wanted to check if anyone has any insights or experience or suggestions in this area.

Thanks in advance for your help.  Really want that hardware acceleration -- surprise, surprise! ;-)

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