Re: Mapping large framebuffers into kernel space

[Jon Smirl]

--- Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> The kernel has 4Gb of virtual address space. Because of the way x86
> works it really wants to keep the user map, the view of main memory and 
> io mappings visible at once. For larger objects you have to use kmap and
> map them through a window (anyone remember they joys of EMS). On
> 64bit this of course all goes away
> 

On my system I have 1GB physical and 1GB swap. So there should always be some
open address space in the 1-4GB kernel address space. Would it be better to map
the framebuffer to 1-4GB when HIGHMEM is configured? Is there an ioremap() that
will map to high memory? Seems that this would be better than reserving 256MB
in the 0-1GB range and forcing 256MB of physical RAM into highmem.

The kernel DRM drivers map framebuffers up to 256MB in size into user space.
Could this be mapped as a single 256MB page instead of 64K 4KB ones?

We're working on the radeon drivers right now so I can try a few things out.

=====
Jon Smirl
jonsmirl@xxxxxxxxx

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