Comment # 7 on bug 1168776 from Achim Gratz

I updated my other Tumbleweed machine to 5.6.0 today (it's also a Haswell, but
only an i3-4130 and FullHD display).  Here the FBC is not on by default:

# cat /sys/kernel/debug/dri/0/i915_gem_objects 
255 shrinkable [0 free] objects, 139313152 bytes
system: total:0x00000001e85dd000, available:0x00000001e85dd000 bytes
stolen: total:0x0000000002000000, available:0x0000000002000000 bytes

# cat /sys/kernel/debug/dri/0/i915_fbc_status 
FBC disabled: disabled at runtime per module param

I can manually switch it on via module parameter in sysfs interface:

# cat /sys/kernel/debug/dri/0/i915_fbc_status 
FBC enabled
Compressing: yes

No messages about "reducing compressed framebuffer size".

# lspci -vv -s 00:02.0
00:02.0 VGA compatible controller: Intel Corporation 4th Generation Core
Processor Family Integrated Graphics Controller (rev 06) (prog-if 00 [VGA
controller])
        DeviceName:  Onboard IGD
        Subsystem: ASUSTeK Computer Inc. Device 8534
        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
        Interrupt: pin A routed to IRQ 29
        Region 0: Memory at f7800000 (64-bit, non-prefetchable) [size=4M]
        Region 2: Memory at e0000000 (64-bit, prefetchable) [size=256M]
        Region 4: I/O ports at f000 [size=64]
        [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
        Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
                Address: fee04004  Data: 4026
        Capabilities: [d0] Power Management version 2
                Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA
PME(D0-,D1-,D2-,D3hot-,D3cold-)
                Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
        Capabilities: [a4] PCI Advanced Features
                AFCap: TP+ FLR+
                AFCtrl: FLR-
                AFStatus: TP-
        Kernel driver in use: i915
        Kernel modules: i915