only 64 out of 128 MB video RAM memory used - why?

[Alex Deucher]

On Mon, Jan 5, 2009 at 3:55 PM, Tomasz Chmielewski <mangoo at wpkg.org> wrote:
> I have a Radeon 9200 PCI video card.
>
> I noticed only 64 MB out of 128 MB of video RAM memory is used:
>
> (II) RADEON(0): Generation 2 PCI interface, using max accessible memory
> (II) RADEON(0): Detected total video RAM=131072K, accessible=65536K (PCI BAR=65536K)
> (--) RADEON(0): Mapped VideoRAM: 65536 kByte (64 bit DDR SDRAM)
>
> Why is it so?
>

The PCI BAR size is only 64 MB so that's the most we can access.  The
GPU can access the rest; it's just the CPU that's limited to 64 MB.
Unfortunately, we need proper memory management to handle the non-CPU
addressable vram for things like software access.  Work has begun on
adding proper memory management to the drm, so it will be supported
eventually.

>
> The system has also AGP card with 256 MB memory, and full 256 MB is used there.

On that card the PCI BAR is 256 MB so the CPU can access the full
amount of vram.

Alex