Re: Programmable BARS

["J. J. Farrell" <jjf@hal.com>]

> From: Henry Gong <hgong@cisco.com>
> 
> If you map these memories in one BAR, the whole allocated memory is still
> fully under the control of your driver. This has been always the way how we
> use the BAR in my previous PCI projects. And this is why I do not
> understand why 6 BARs are available in configuration space. Can anybody
> lighten me please.

Your device may, for whatever reason, have discontiguous address
spaces - a video card with a block of control registers and a frame
buffer is the classic example. Some may be I/O space, some may be
memory. Some of the memory may be prefetchable, some of it may not.
There are only 6 BARs available if none of them support a 64-bit
address space - there's a maximum of 3 if all support 64 bit.