drm/mgag200: Fix big-endian support

[Christian Zigotzky <chzigotzky@xenosoft.de>]

Hello René,

Many thanks for your patch. [1]

I have bought the PCI graphics card Matrox G200 G2+/QUADP-PL/7 32MB with 4x DVI. It is an AGP card connected via PCI. 

We use the new DRM driver MGAG200 since the kernel 7.2.0-rc4 and the old DRM legacy driver for Matrox g200/g400 graphics cards since the stable long-term kernel 5.10.260.

I tested it with the RC5 of kernel 7.2 in my PowerPC machine (e5500) today. Unfortunately, the DRM driver mgag200 can't read the PCI ROM. Maybe only an x86 ROM?

xrandr detects the ports but reports that they are not connected, even though the cables are plugged in.

I also tested it with the stable long-term kernel 5.10.261 with the old legacy DRM drivers for Matrox graphics cards.
I installed the Xorg MGA server xf86-video-mga-2.0.0_3 for the old legacy DRM driver but unfortunately I get only a black screen.

Is it possible to use this card with PPC Linux?

More information:

lspci -vvv

0001:05:00.0 VGA compatible controller: Matrox Electronics Systems Ltd. MGA G200 AGP (rev 03) (prog-if 00 [VGA controller])
	Subsystem: Matrox Electronics Systems Ltd. G200 Multi-Monitor
	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 128 (4000ns min, 8000ns max), Cache Line Size: 32 bytes
	Interrupt: pin A routed to IRQ 18
	Region 0: Memory at c20000000 (32-bit, prefetchable) [size=16M]
	Region 1: Memory at c21000000 (32-bit, non-prefetchable) [size=16K]
	Region 2: Memory at c21800000 (32-bit, non-prefetchable) [size=8M]
	Expansion ROM at c21010000 [disabled] [size=64K]
	Capabilities: [dc] Power Management version 1
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [f0] AGP version 1.0
		Status: RQ=32 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW- AGP3- Rate=x1,x2
		Command: RQ=1 ArqSz=0 Cal=0 SBA- AGP- GART64- 64bit- FW- Rate=<none>
	Kernel driver in use: mgag200

0001:05:04.0 Display controller: Matrox Electronics Systems Ltd. MGA G200 AGP (rev 03)
	Subsystem: Matrox Electronics Systems Ltd. G200 Multi-Monitor
	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 128 (4000ns min, 8000ns max), Cache Line Size: 32 bytes
	Interrupt: pin A routed to IRQ 18
	Region 0: Memory at c22000000 (32-bit, prefetchable) [size=16M]
	Region 1: Memory at c23000000 (32-bit, non-prefetchable) [size=16K]
	Region 2: Memory at c23800000 (32-bit, non-prefetchable) [size=8M]
	Expansion ROM at c21020000 [disabled] [size=64K]
	Capabilities: [dc] Power Management version 1
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [f0] AGP version 1.0
		Status: RQ=32 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW- AGP3- Rate=x1,x2
		Command: RQ=1 ArqSz=0 Cal=0 SBA- AGP- GART64- 64bit- FW- Rate=<none>
	Kernel driver in use: mgag200

0001:05:08.0 Display controller: Matrox Electronics Systems Ltd. MGA G200 AGP (rev 03)
	Subsystem: Matrox Electronics Systems Ltd. G200 Multi-Monitor
	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 128 (4000ns min, 8000ns max), Cache Line Size: 32 bytes
	Interrupt: pin A routed to IRQ 18
	Region 0: Memory at c24000000 (32-bit, prefetchable) [size=16M]
	Region 1: Memory at c25000000 (32-bit, non-prefetchable) [size=16K]
	Region 2: Memory at c25800000 (32-bit, non-prefetchable) [size=8M]
	Expansion ROM at c21030000 [disabled] [size=64K]
	Capabilities: [dc] Power Management version 1
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [f0] AGP version 1.0
		Status: RQ=32 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW- AGP3- Rate=x1,x2
		Command: RQ=1 ArqSz=0 Cal=0 SBA- AGP- GART64- 64bit- FW- Rate=<none>
	Kernel driver in use: mgag200

0001:05:0c.0 Display controller: Matrox Electronics Systems Ltd. MGA G200 AGP (rev 03)
	Subsystem: Matrox Electronics Systems Ltd. G200 Multi-Monitor
	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 128 (4000ns min, 8000ns max), Cache Line Size: 32 bytes
	Interrupt: pin A routed to IRQ 18
	Region 0: Memory at c26000000 (32-bit, prefetchable) [size=16M]
	Region 1: Memory at c27000000 (32-bit, non-prefetchable) [size=16K]
	Region 2: Memory at c27800000 (32-bit, non-prefetchable) [size=8M]
	Expansion ROM at c21040000 [disabled] [size=64K]
	Capabilities: [dc] Power Management version 1
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [f0] AGP version 1.0
		Status: RQ=32 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW- AGP3- Rate=x1,x2
		Command: RQ=1 ArqSz=0 Cal=0 SBA- AGP- GART64- 64bit- FW- Rate=<none>
	Kernel driver in use: mgag200


dmesg | grep -i mga

[    2.302206] [drm] Initialized mgag200 1.0.0 for 0001:05:00.0 on minor 1
[    2.303761] mgag200 0001:05:00.0: [drm] Cannot find any crtc or sizes
[    2.304697] mgag200 0001:05:04.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
[    2.305792] [drm] Initialized mgag200 1.0.0 for 0001:05:04.0 on minor 2
[    2.308281] mgag200 0001:05:04.0: [drm] Cannot find any crtc or sizes
[    2.308802] mgag200 0001:05:08.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
[    2.309319] [drm] Initialized mgag200 1.0.0 for 0001:05:08.0 on minor 3
[    2.309785] mgag200 0001:05:00.0: [drm] Cannot find any crtc or sizes
[    2.310900] mgag200 0001:05:08.0: [drm] Cannot find any crtc or sizes
[    2.311895] mgag200 0001:05:0c.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
[    2.312633] [drm] Initialized mgag200 1.0.0 for 0001:05:0c.0 on minor 4
[    2.312844] mgag200 0001:05:04.0: [drm] Cannot find any crtc or sizes
[    2.315512] mgag200 0001:05:0c.0: [drm] Cannot find any crtc or sizes
[    2.317178] mgag200 0001:05:08.0: [drm] Cannot find any crtc or sizes
[    2.323318] mgag200 0001:05:0c.0: [drm] Cannot find any crtc or sizes

xrandr

…

VGA-4-4 disconnected (normal left inverted right x axis y axis)
VGA-3-3 disconnected (normal left inverted right x axis y axis)
VGA-2-2 disconnected (normal left inverted right x axis y axis)
VGA-1-1 disconnected (normal left inverted right x axis y axis)

…

lspci -nnk | grep VGA

0001:05:00.0 VGA compatible controller [0300]: Matrox Electronics Systems Ltd. MGA G200 AGP [102b:0521] (rev 03)

Thanks,
Christian

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/gpu/drm/mgag200/mgag200_mode.c?id=6cb31fba137d45e682ce455b8ea364f44d5d4f98