Asus Eee PC 1225b

Graphics with open-source radeon drivers
All the necessary firmware is provided with package (it is easy to emerge within a chrooted environment):

Kernel parameters are well described in the article about Radeon. However the choice of firmware isn't that obvious. As it is supposed here, APU is usually detected as PALM, while in fact it is closer to SUMO. The only way out is to compile them both into kernel:

This lets kernel modesetting work properly.

ALSA configuration
A good way to manage ALSA is to emerge alsa-utils:

To start alsa at boot time type:

There is a problem that actually ALSA often sees two sound cards: HD-Audio Generic (that is a kind of a virtual device, i.e. it doesn't actually play music) and the required HDA ATI SB. The simplest way to check it is to launch

If HD-Audio Generic is the first number, it might be the default card. If it is the case, than you're likely to have no sound unless the default card is switched from 0 to 1.