On Mon, 26 Apr 2004, Stefan Reinauer wrote:
Devices with bus master set are allowed to DMA into main memory whenever they feel like it so it is dangerous to enable that bit indiscriminately.
--> If at all, it should be done with careful checking.
Here is a possible scenario. You are in linuxbios after somehow falling into it -- i.e., no power up, no reset has happened. Devices for whatever reason are not totally reset, including the ethernet device. The ethernet device is the kind with on-chip buffer queue pointerss. You enable bus master. Chip gets a broadcast packet. It writes it somewhere to memory, over code that won't get run in 2 or 3 weeks. 2 or 3 weeks later, the code is executed.
Your kernel goes kaboom!
How do you figure out what happened? This is a possible scenario that can happen once you start enabling bus master in the bios.
ron