Re: PCI Express support for 2.4 kernel

Alan Cox
2003-12-15T19:24:17Z

> It looks confusing. On my test system (don't ask details, I am not
> alowed to share this info), I see
> video controller with 256Mb BAR. Does it mean this controller will not
> work as well?

The 256Mb BAR turns up in a variety of graphic cards, and 512Mb in a few.
The kernel maps just enough memory for the frame buffer + cache. There isn't
enough space to map it all. User space apps may well have the 512Mb mapped
into their address space, but that isnt the kernel one

> There is alternative solution, for each transaction to ioremap/unmap
> corresponded page.
> I don't like it, it involves huge overhead.

ioremap means you can't use pci_exp_* from an interrupt so kmap is probably
needed. It is overhead but the design of the 386 left us with that problem on
x86 platforms and it isnt going to go away. On ia64/x86_64 etc its a non issue