Ubuntu – Max VRAM supported by open source ATI radeon


I have an ATI HD6370 with dedicated 1G running on Ubuntu 11.10. Following is the output from dmesg

sourajit@sourajit:/etc/X11$ sudo dmesg | grep drm
[    5.149765] [drm] Initialized drm 1.1.0 20060810
[    5.606144] [drm] radeon defaulting to kernel modesetting.
[    5.606147] [drm] radeon kernel modesetting enabled.
[    5.606436] [drm] initializing kernel modesetting (CEDAR 0x1002:0x68E4 0x17AA:0x397A).
[    5.606630] [drm] register mmio base: 0xE0600000
[    5.606631] [drm] register mmio size: 131072
[    6.475815] [drm] Detected VRAM RAM=1024M, BAR=256M
[    6.475819] [drm] RAM width 64bits DDR
[    6.475890] [drm] radeon: 1024M of VRAM memory ready
[    6.475891] [drm] radeon: 512M of GTT memory ready.

However, this is the output of lspci, post install. What does this imply ? How much memory is radeon actually using ?

01:00.0 VGA compatible controller: ATI Technologies Inc Robson CE [AMD Radeon HD 6300 Series] (prog-if 00 [VGA controller])
    Subsystem: Lenovo Device 397a
    Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
    Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 0, Cache Line Size: 64 bytes
    Interrupt: pin A routed to IRQ 42
    **Region 0: Memory at c0000000 (64-bit, prefetchable) [size=256M]
    Region 2: Memory at e0600000 (64-bit, non-prefetchable) [size=128K]**
    Region 4: I/O ports at 3000 [size=256]
    Expansion ROM at e0620000 [disabled] [size=128K]

Best Answer

It is using 1024M. The 256M is just the limit of how much the CPU can directly address. The rest of the ram is available to the GPU and the CPU doesn't need to be able to directly touch it.

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