Thinkpad X1 Carbon 3rd - Reducing the compressed framebuffer size

[Ville Syrjälä]

On Tue, Feb 13, 2018 at 09:50:30AM +0100, Pali Rohár wrote:
> On Tuesday 06 February 2018 16:21:43 Pali Rohár wrote:
> > Hi! I'm periodically getting following message in dmesg on Lenovo
> > Thinkpad X1 Carbon 3rd generation:
> > 
> > [drm] Reducing the compressed framebuffer size. This may lead to less power savings than a non-reduced-size. Try to increase stolen memory size if available in BIOS.
> > 
> > In BIOS I already set GPU size to 512M, but this did not help. Also
> > update to last BIOS version did not help.
> > 
> > So why this message is periodically print in dmesg? And what can I do
> > with this problem?
> > 
> > And why cannot Linux kernel allocate itself more memory for GPU (if BIOS
> > can/could do that)? Is not 512MB for GPU enough?
> 
> And here is output from lspci, which clearly says that 512MB is already
> set for GPU:

The PCI BAR size has nothing to do with the size of the stolen memory.
The BAR just provides a window into the global GTT address space of the
GPU. Stolen memory is a contiguous chunk of physical memory carved out
by the BIOS. The BIOS may or may not provide a knob to change the size
of the stolen memory.

> 
> $ lspci -v -s 00:02.0
> 00:02.0 VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) (prog-if 00 [VGA controller])
>         Subsystem: Lenovo HD Graphics 5500
>         Flags: bus master, fast devsel, latency 0, IRQ 46
>         Memory at e0000000 (64-bit, non-prefetchable) [size=16M]
>         Memory at c0000000 (64-bit, prefetchable) [size=512M]
>         I/O ports at 3000 [size=64]
>         [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
>         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
>         Kernel modules: i915
> 
> -- 
> Pali Rohár
> pali.rohar at gmail.com
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-- 
Ville Syrjälä
Intel OTC