macppc 4K monitor support regressed from 9.99.99 -> 10.0_BETA

[Tom Lane <tgl%sss.pgh.pa.us@localhost>]

I have a 4K monitor plugged into a G4 tower via an HDMI->DVI cable.
NetBSD was able to display on that monitor as recently as 9.99.99
from mid-August; but a build from the current netbsd-10 snapshot
(202212262100Z) seems to fail to sync.  The monitor keeps waking up,
displaying "no signal", and going back to sleep, every 30 seconds or so.

Here's the relevant part of dmesg, if that helps:

[     1.000000] uninorth0 at mainbus0
[     1.000000] pci0 at uninorth0 bus 0
[     1.000000] pci0: i/o space, memory space enabled
[     1.000000] pchb0 at pci0 dev 11 function 0
[     1.000000] pchb0: Apple Computer UniNorth AGP Bridge (rev. 0x00)
[     1.000000] radeonfb0 at pci0 dev 16 function 0: ATI Technologies Radeon 9000/PRO If (rev. 0x01)
[     1.000000] trying to read disabled BIOS...
[     1.000000] radeonfb0: No video BIOS, using default clocks
[     1.000000] radeonfb0: refclk = 27.000 MHz, refdiv = 12 minpll = 125000, maxpll = 400000
[     1.000000] radeonfb0: 64 MB aperture at 0x98000000, 64 KB registers at 0x90000000
[     1.000000] radeonfb0: display 0: initial virtual resolution 640x480 at 8 bpp
[     1.000000] radeonfb0: using 32 MB per display
[     1.000000] radeonfb0: port 0: physical 640x480 60Hz
[     1.000000] radeonfb0: port 1: physical 640x480 60Hz
[     1.000000] wsdisplay0 at radeonfb0 kbdmux 1: console (fb, vt100 emulation)
[     1.000000] wsmux1: connecting to wsdisplay0
[     1.000000] drm at radeonfb0 not configured
[     1.000000] uninorth1 at mainbus0
[     1.000000] pci1 at uninorth1 bus 0
[     1.000000] pci1: i/o space, memory space enabled
[     1.000000] pchb1 at pci1 dev 11 function 0
[     1.000000] pchb1: Apple Computer UniNorth Host-PCI Bridge (rev. 0x00)
[     1.000000] obio0 at pci1 dev 23 function 0: addr 0x80000000
[     1.000000] obio0: enabling KeyLargo internal modem
[     1.000000] zsc0 at obio0 irq 22,23
[     1.000000] zstty0 at zsc0 channel 0
[     1.000000] zstty1 at zsc0 channel 1
[     1.000000] snapper0 at obio0 offset 0x10000: irq 30,1,2
[     1.000000] pmu0 at obio0 offset 0x16000 irq 47:  rev. 12
[     1.000000] pmu0: initializing IIC bus

I do get a good display with a smaller monitor (1920x1080) plugged into
the same port, but that's not very convenient for assorted reasons.

Any thoughts about where the relevant change might lie?

			regards, tom lane