I have a couple of HD5450 cards with pci id 1002:68e1 subsystem 1787:3000.
These are HD5450 cards, even though 1002:68e1 is the pci id of HD5430 Mobility.
One card is marketed as HIS H545HO512, the other as ASUS EAH5450 SL/DI/512MD3/MG(LP).  (I also have another HIS H545HO512 card that reports
the correct pci id 1002:68f9, and therefore not all these HIS cards are the same.)

The bug is that the kernel radeon driver sets the RADEON_IS_MOBILITY flag for the 1002:68e1 cards, which prevents the power profiles from working correctly.  My diagnosis of the problem is that the driver looks up the battery power profile, which does not exist, and it falls back to the default power profile, which runs at full speed all the time.  I have verified that by clearing the RADEON_IS_MOBILITY flag and recompiling the kernel module, this command works as expected:

  echo "low" > /sys/class/drm/card0/device/power_profile

Since these cards with the wrong PCI ID seem common (the two cheapest cards on newegg have this issue), it would be nice if future kernels could provide a workaround.

Thanks,
Matteo Frigo