nv driver can't use dpms on GeForce FX Go 5200

The 'nv' driver on this Dell Inspiron 5150 (with a GeForce FX Go 5200) can't
seem to do DPMS. If dpms kicks in, the screen goes blank, then white fades in
from around the edges. This happens with 'xset dpms force off', 'xset dpms force
standby' or 'xset dpms force suspend', although acpi suspend works fine (so long
as I use "vbetool post" on un-suspend). For force standby and force suspend, the
screen isn't blanked before the white starts fading in from the edges.

The nvidia driver does dpms correctly (but many other things wrong). Hardware
bits from Xorg log:
(==) ServerLayout "Default Layout"
(**) |-->Screen "Default Screen" (0)
(**) | |-->Monitor "Generic Monitor"
(**) | |-->Device "NVIDIA Corporation NV34M [GeForce FX Go 5200]"

(II) Primary Device is: PCI 01:00:0
(--) Chipset GeForce FX Go5200 found

(II) NV(0): Initializing int10
(II) NV(0): Primary V_BIOS segment is: 0xc000
(--) NV(0): Chipset: "GeForce FX Go5200"
(**) NV(0): Depth 24, (--) framebuffer bpp 32
(==) NV(0): RGB weight 888
(==) NV(0): Default visual is TrueColor
(II) Loading sub module "vgahw"
(II) LoadModule: "vgahw"
(II) Loading /usr/X11R6/lib/modules/libvgahw.a
(II) Module vgahw: vendor="X.Org Foundation"
        compiled for 6.8.2, module version = 0.1.0
        ABI class: X.Org Video Driver, version 0.7
(==) NV(0): Using HW cursor
(--) NV(0): Linear framebuffer at 0xD0000000
(--) NV(0): MMIO registers at 0xFC000000

(II) Reloading /usr/X11R6/lib/modules/libddc.a
(II) NV(0): I2C bus "DDC" initialized.
(II) NV(0): Probing for analog device on output A...
(--) NV(0): ...can't find one
(II) NV(0): Probing for analog device on output B...
(--) NV(0): ...can't find one
(II) NV(0): Probing for EDID on I2C bus A...
(II) NV(0): I2C device "DDC:ddc2" registered at address 0xA0.
(II) NV(0): I2C device "DDC:ddc2" removed.
(II) NV(0): ... none found
(II) NV(0): Probing for EDID on I2C bus B...
(II) NV(0): I2C device "DDC:ddc2" registered at address 0xA0.
(II) NV(0): I2C device "DDC:ddc2" removed.
(II) NV(0): ... none found
(--) NV(0): CRTC 0 is currently programmed for DFP
(II) NV(0): Using DFP on CRTC 0
(--) NV(0): Panel size is 1600 x 1200
(--) NV(0): VideoRAM: 65536 kBytes
(==) NV(0): Using gamma correction (1.0, 1.0, 1.0)
(II) NV(0): Generic Monitor: Using hsync range of 30.00-75.00 kHz
(II) NV(0): Generic Monitor: Using vrefresh range of 50.00-85.00 Hz
(II) NV(0): Clock range: 12.00 to 350.00 MHz
(II) NV(0): Not using default mode "320x175" (bad mode
clock/interlace/doublescan) [lots of these]

(--) NV(0): Virtual size is 1600x1200 (pitch 1600)
(**) NV(0): *Default mode "1600x1200": 162.0 MHz, 75.0 kHz, 60.0 Hz
(II) NV(0): Modeline "1600x1200" 162.00 1600 1664 1856 2160 1200 1201 1204
1250 +hsync
+vsync

(**) Option "dpms"
(**) NV(0): DPMS enabled

That's all I could see that was relevant.