amd64 DRMKMS Radeon HD 4550 firmware_open(radeondrmkms/radeon/RV710_pfp.bin) called too early

[David Shao <davshao%gmail.com@localhost>]

Using latest NetBSD source updated through

Module Name:    src
Date:           Tue Jul 22 04:55:51 UTC 2014

Modified Files:
        src/sys/dev/sbus: tcx.c

amd64 DRMKMS on a machine with a Sapphire Radeon HS 4550 fails to
finish booting with:

drm:initializing kernel modesetting (RV710 0x1002:0x9540 0x174B:0xE970).
drm: register mmio base: 0xf7e20000
drm: register mmio size: 65536
drm kern info: ATOM BIOS: 11X
radeondrmkms0: info: VRAM: 512M 0x0000000000000000 -
0x000000001FFFFFFF (512M used)
radeondrmkms0: info: GTT: 1024M 0x0000000020000000 - 0x000000005FFFFFFF
drm: Detected VRAM RAM=200M, BAR=256M
drm: RAM width 64 bits DDR
Zone  kernel: Available graphics memory: 5777944 kiB
Zone   dma32: Available graphics memory: 2097152 kiB
drm: radeon: 512M of VRAM memory ready
drm: radeon: 1024M of GTT memory ready
drm: Loading RV710 Microcode
firmware_open(radeondrmkms/radeon/RV710_pfp.bin) called too early
drm kern error: r600_cp: Failed to load firmware "radeon/RV710_pfp.bin"
DRM error in rv770_init: Failed to load firmware!
: error: Fatal error during GPU init
radeondrmkms0: unable to attach drm: 2
...
audio1 at pad0: half duplex, playback, capture
boot device: wd2
root on wd2a dumps on wd2b
dump_misc_init: max_paddr = 0x41f000000
mountroot: trying smbfs...
mountroot: trying ntfs...
mountroot: trying nfs...
mountroot: trying msdos...
mountroot: trying lfs...
mountroot: trying ext2fs...
mountroot: trying ffs...
root file system type: ffs
init: copying out path `/sbin/init' 11
panic: cnopen: no console device
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip fffffff8028acbd cs 8 rflags 246 cr2 7f7ffc60cb88 ilevel
0 rsp fffffe811d9e4ad8
curlwp 0xfffffe811d899260 pid 2.1 lowest kstack 0xfffffi811d9e12c0
Stopped in pid 2.1 (init) at   netbsd:breakpoint+0x5:  leave

In the still-working GENERIC:

vga0 at pci4 dev 0 function 0: vendor 0x1002 product 0x9540 (rev. 0x00)
wsdisplay0 at vga0 kbdmux 1: console (80x25, vt100 emulation)
wsmux1: connecting to wsdisplay0
radeondrm0 at vga0: ATI Radeon HD 4550
radeondrm0: Initialized radeon 1.29.0 20080613
...
root on wd2a dumps on wd2b
root file system type: ffs
info: [drm] Setting GART location based on new memory map
info: [drm] Loading RV710 Microcode
info: [drm] Resetting GPU
info: [drm] writeback test succeeded in 2 usecs
radeondrm0: interrupting at ioapic0 pin 19