[coreboot] Haswell/panther - GPU memory allocation

[Matt DeVillier]

Greetings!

I'm looking to adjust the amount of system memory allocated to the GPU on panther (Haswell mobile), since certain applications (eg, Steam) report a suboptimal amount of GPU memory.  lspci reports the following:

00:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated Graphics Controller (rev 09) (prog-if 00 [VGA controller])
        Subsystem: Intel Corporation Haswell-ULT Integrated Graphics Controller
        Flags: bus master, fast devsel, latency 0, IRQ 43
        Memory at e0000000 (64-bit, non-prefetchable) [size=4M]
        Memory at d0000000 (64-bit, prefetchable) [size=256M]
        I/O ports at 3000 [size=64]
        Expansion ROM at <unassigned> [disabled]
        Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
        Capabilities: [d0] Power Management version 2
        Capabilities: [a4] PCI Advanced Features
        Kernel driver in use: i915

Looking at src/northbridge/intel/haswell/early_init.c, the 256M appears to correlate to the MSAC register, and going by Intel's datasheet, setting the MSAC to 0x6 (from the current value of 0x2) should increase the allocation to 512MB, yet doing so appears to have no affect (at least as far as lspci is concerned).

I also looked at the GMS portion of the GGC register, which is currently set to 32MB, but changing it, either in conjunction with or separately from MSAC, has no discernible effect either.

Obviously there's something else I'm missing, so would appreciate any help.

thanks,
Matt