Limiting BAR resource region size allocation (device claims 2x what it needs) ?

[TJ <tj@iam.tj>]

Is there a way to over-ride a device's BAR region-size allocation? I've been looking but the only way I can identify is via a quirk.

I'm dealing with a Nvidia GeForce Go 7600 (NV8B) in a Sony Vaio VGN-FE41Z laptop. The device requests and is assigned a VRAM window of 256MB. However, there is only 128MB of physical VRAM.

>From my research it seems that some versions of the Go 7600 did have 256MB VRAM and the device is programmed
to request that regardless of the physically installed VRAM.

Combined with other PCI devices in the system the assignment of a 256MB window means that maximum RAM in the laptop is severely limited.

The CPU is 64-bit but the i945PM northbridge is 32-bit (so no physical > 4GB addressing). With PCI allocations as they are the system is limited to 2GB of RAM under Linux (3GB on Windows Vista).


$ sudo lspci -vnn -s 01:00.0
01:00.0 VGA compatible controller [0300]: NVIDIA Corporation G73 [GeForce Go 7600] [10de:0398] (rev a1) (prog-if 00 [VGA controller])
	Subsystem: Sony Corporation Device [104d:81ef]
	Flags: bus master, fast devsel, latency 0, IRQ 16
	Memory at d5000000 (32-bit, non-prefetchable) [size=16M]
	Memory at b0000000 (64-bit, prefetchable) [size=256M]
	Memory at d4000000 (64-bit, non-prefetchable) [size=16M]
	I/O ports at 2000 [disabled] [size=128]
	Expansion ROM at <unassigned> [disabled]
	Capabilities: [60] Power Management version 2
	Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
	Capabilities: [78] Express Endpoint, MSI 00
	Capabilities: [100] Virtual Channel
	Capabilities: [128] Power Budgeting <?>
	Kernel driver in use: nvidia
	Kernel modules: nvidia_current_updates, nouveau, nvidiafb