Why is mgag200 not used over matroxfb? (was: matroxfb: cannot determine memory size)

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Thomas,


Thank you for your reply.

Am 16.12.22 um 13:27 schrieb Thomas Zimmermann:

> Am 15.12.22 um 17:39 schrieb Paul Menzel:

[…]

>> Between Linux 5.10.103 and 5.10.110/5.15.77, matrixfb fails to load.
> 
> Off-topic, but related. matroxfb is obsolete and there's a maintained 
> DRM replacement (mgag200) for this hardware.

I also remembered something like this in the back of my head. Though I 
thought about using simpledrm (`DRM_SIMPLEDRM`), we do not build though.

> Is there anything missing from mgag200 that prevents you from switching?
No, it looks like the matroxfb modules take precedence over the mgag200 
module:

     $ grep -e FB_MATROX -e MGAG /boot/config-5.15.77.mx64.440
     CONFIG_DRM_MGAG200=m
     CONFIG_FB_MATROX=m
     CONFIG_FB_MATROX_MILLENIUM=y
     CONFIG_FB_MATROX_MYSTIQUE=y
     CONFIG_FB_MATROX_G=y
     CONFIG_FB_MATROX_I2C=m
     # CONFIG_FB_MATROX_MAVEN is not set

     $ lsmod | grep matrox
     matroxfb_base          28672  0
     matroxfb_g450          16384  1 matroxfb_base
     matroxfb_Ti3026        16384  1 matroxfb_base
     matroxfb_accel         16384  1 matroxfb_base
     matroxfb_DAC1064       20480  1 matroxfb_base
     g450_pll               16384  2 matroxfb_g450,matroxfb_DAC1064
     matroxfb_misc          20480  5 
g450_pll,matroxfb_Ti3026,matroxfb_base,matroxfb_g450,matroxfb_DAC1064


Kind regards,

Paul


PS: Output of `modinfo`:

```
$ modinfo matroxfb_base
filename: 
/lib/modules/5.15.77.mx64.440/kernel/drivers/video/fbdev/matrox/matroxfb_base.ko
license:        GPL
description:    Accelerated FBDev driver for Matrox 
Millennium/Mystique/G100/G200/G400/G450/G550
author:         (c) 1998-2002 Petr Vandrovec <vandrove@vc.cvut.cz>
alias:          pci:v0000102Bd00002527sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000525sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000521sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000532sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000520sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00001001sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00001000sv*sd*bc*sc*i*
alias:          pci:v0000102Bd0000051Asv*sd*bc*sc*i*
alias:          pci:v0000102Bd0000051Fsv*sd*bc*sc*i*
alias:          pci:v0000102Bd0000051Bsv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000519sv*sd*bc*sc*i*
depends: 
matroxfb_g450,matroxfb_misc,matroxfb_DAC1064,matroxfb_Ti3026,matroxfb_accel
retpoline:      Y
intree:         Y
name:           matroxfb_base
vermagic:       5.15.77.mx64.440 SMP mod_unload modversions
parm:           mem:Size of available memory in MB, KB or B 
(2,4,8,12,16MB, default=autodetect) (int)
parm:           disabled:Disabled (0 or 1=disabled) (default=0) (int)
parm:           noaccel:Do not use accelerating engine (0 or 1=disabled) 
(default=0) (int)
parm:           nopan:Disable pan on startup (0 or 1=disabled) 
(default=0) (int)
parm:           no_pci_retry:PCI retries enabled (0 or 1=disabled) 
(default=0) (int)
parm:           novga:VGA I/O (0x3C0-0x3DF) disabled (0 or 1=disabled) 
(default=0) (int)
parm:           nobios:Disables ROM BIOS (0 or 1=disabled) (default=do 
not change BIOS state) (int)
parm:           noinit:Disables W/SG/SD-RAM and bus interface 
initialization (0 or 1=do not initialize) (default=0) (int)
parm:           memtype:Memory type for G200/G400 (see 
Documentation/fb/matroxfb.rst for explanation) (default=3 for G200, 0 
for G400) (int)
parm:           mtrr:This speeds up video memory accesses (0=disabled or 
1) (default=1) (int)
parm:           sgram:Indicates that G100/G200/G400 has SGRAM memory 
(0=SDRAM, 1=SGRAM) (default=0) (int)
parm:           inv24:Inverts clock polarity for 24bpp and loop 
frequency > 100MHz (default=do not invert polarity) (int)
parm:           inverse:Inverse (0 or 1) (default=0) (int)
parm:           dev:Multihead support, attach to device ID (0..N) 
(default=all working) (int)
parm:           vesa:Startup videomode (0x000-0x1FF) (default=0x101) (int)
parm:           xres:Horizontal resolution (px), overrides xres from 
vesa (default=vesa) (int)
parm:           yres:Vertical resolution (scans), overrides yres from 
vesa (default=vesa) (int)
parm:           upper:Upper blank space (scans), overrides upper from 
vesa (default=vesa) (int)
parm:           lower:Lower blank space (scans), overrides lower from 
vesa (default=vesa) (int)
parm:           vslen:Vertical sync length (scans), overrides lower from 
vesa (default=vesa) (int)
parm:           left:Left blank space (px), overrides left from vesa 
(default=vesa) (int)
parm:           right:Right blank space (px), overrides right from vesa 
(default=vesa) (int)
parm:           hslen:Horizontal sync length (px), overrides hslen from 
vesa (default=vesa) (int)
parm:           pixclock:Pixelclock (ns), overrides pixclock from vesa 
(default=vesa) (int)
parm:           sync:Sync polarity, overrides sync from vesa 
(default=vesa) (int)
parm:           depth:Color depth (0=text,8,15,16,24,32) (default=vesa) 
(int)
parm:           maxclk:Startup maximal clock, 0-999MHz, 1000-999999kHz, 
1000000-INF Hz (int)
parm:           fh:Startup horizontal frequency, 0-999kHz, 1000-INF Hz (int)
parm:           fv:Startup vertical frequency, 0-INF Hz
You should specify 
"fv:max_monitor_vsync,fh:max_monitor_hsync,maxclk:max_monitor_dotclock" 
(int)
parm:           grayscale:Sets display into grayscale. Works perfectly 
with paletized videomode (4, 8bpp), some limitations apply to 16, 24 and 
32bpp videomodes (default=nograyscale) (int)
parm:           cross4MB:Specifies that 4MB boundary can be in middle of 
line. (default=autodetected) (int)
parm:           dfp:Specifies whether to use digital flat panel 
interface of G200/G400 (0 or 1) (default=0) (int)
parm:           dfp_type:Specifies DFP interface type (0 to 255) 
(default=read from hardware) (int)
parm:           outputs:Specifies which CRTC is mapped to which output 
(string of up to three letters, consisting of 0 (disabled), 1 (CRTC1), 2 
(CRTC2)) (default=111 for Gx50, 101 for G200/G400 with DFP, and 100 for 
all other devices) (string)
```

```
$ modinfo mgag200
filename: 
/lib/modules/5.15.77.mx64.440/kernel/drivers/gpu/drm/mgag200/mgag200.ko
license:        GPL
description:    MGA G200 SE
author:         Matthew Garrett
alias:          pci:v0000102Bd00000538sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000536sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000534sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000533sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000532sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000530sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000524sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000522sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000521sv*sd*bc*sc*i*
alias:          pci:v0000102Bd00000520sv*sd*bc*sc*i*
depends:        drm,drm_kms_helper,i2c-algo-bit
retpoline:      Y
intree:         Y
name:           mgag200
vermagic:       5.15.77.mx64.440 SMP mod_unload modversions
parm:           modeset:Disable/Enable modesetting (int)
```