Trying to make do with Linux's page allocation interface is pretty
much always wrong: either we let uvm allocate pages in uvm objects
for us, or we use bus_dma.
Screen blanks on boot on the Ivy Bridge system with
DRM error in cpt_serr_int_handler: PCH transcoder A FIFO underrun
But after that everything is OK. Appears to be an upstream problem.
To investigate...
I think there's a cache flushing issue somewhere -- there are little
display artefacts on my T60.
