On 2026/01/27 12:05, Kirill A. Korinsky wrote:
> On Tue, 27 Jan 2026 10:21:02 +0100,
> Crystal Kolipe <kolipe.c@exoticsilicon.com> wrote:
> > 
> > On Tue, Jan 27, 2026 at 03:21:36AM +0100, Kirill A. Korinsky wrote:
> > > The fallback forces VGA text mode even when the VGA probe fails, that
> > > guaranteeing an early console, so boot can proceed even if GOP is absent
> > > and no GPU driver is available.
> > 
> > With this patch, the kernel will be writing to memory locations and I/O ports
> > that are traditionally associated with VGA hardware, despite no VGA hardware
> > (or emulation thereof), necessarily being present.

indeed, including some quite common hw

OpenBSD 7.8-current (GENERIC.MP) #210: Fri Jan 16 23:41:52 MST 2026
    deraadt@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP
real mem = 2112446464 (2014MB)
avail mem = 2021711872 (1928MB)
random: good seed from bootblocks
mpath0 at root
scsibus0 at mpath0: 256 targets
mainbus0 at root
bios0 at mainbus0: SMBIOS rev. 3.0 @ 0x7ee97040 (13 entries)
bios0: vendor coreboot version "v4.19.0.1" date 01/31/2023
bios0: PC Engines apu2
acpi0 at bios0: ACPI 6.0
acpi0: sleep states S0 S1 S4 S5
acpi0: tables DSDT FACP SSDT MCFG TPM2 APIC HEST SSDT SSDT DRTM HPET
acpi0: wakeup devices PBR4(S4) PBR5(S4) PBR6(S4) PBR7(S4) PBR8(S4) UOH1(S3) UOH2(S3) UOH3(S3) UOH4(S3) UOH5(S3) UOH6(S3) XHC0(S4)
acpitimer0 at acpi0: 3579545 Hz, 32 bits
acpimcfg0 at acpi0
acpimcfg0: addr 0xf8000000, bus 0-63
acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: AMD GX-412TC SOC, 998.18 MHz, 16-30-01, patch 07030105
cpu0: cpuid 1 edx=178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,MMX,FXSR,SSE,SSE2,HTT> ecx=36d8220b<SSE3,PCLMUL,MWAIT,SSSE3,CX16,SSE4.1,SSE4.2,MOVBE,POPCNT,AES,XSAVE,AVX,F16C>
cpu0: cpuid 6 eax=4<ARAT> ecx=1<EFFFREQ>
cpu0: cpuid 7.0 ebx=8<BMI1>
cpu0: cpuid d.1 eax=1<XSAVEOPT>
cpu0: cpuid 80000001 edx=2fd3fbff<NXE,MMXX,FFXSR,PAGE1GB,RDTSCP,LONG> ecx=1d4037ff<LAHF,CMPLEG,SVM,EAPICSP,AMCR8,ABM,SSE4A,MASSE,3DNOWP,OSVW,IBS,SKINIT,TOPEXT,DBKP,PERFTSC,PCTRL3>
cpu0: cpuid 80000007 edx=33d9<HWPSTATE,ITSC>
cpu0: 32KB 64b/line 8-way D-cache, 32KB 64b/line 2-way I-cache, 2MB 64b/line 16-way L2 cache
cpu0: smt 0, core 0, package 0
mtrr: Pentium Pro MTRR support, 8 var ranges, 88 fixed ranges
cpu0: apic clock running at 99MHz
cpu0: mwait min=64, max=64, IBE
cpu1 at mainbus0: apid 1 (application processor)
cpu1: AMD GX-412TC SOC, 998.25 MHz, 16-30-01, patch 07030105
cpu1: smt 0, core 1, package 0
cpu2 at mainbus0: apid 2 (application processor)
cpu2: AMD GX-412TC SOC, 998.46 MHz, 16-30-01, patch 07030105
cpu2: smt 0, core 2, package 0
cpu3 at mainbus0: apid 3 (application processor)
cpu3: AMD GX-412TC SOC, 998.54 MHz, 16-30-01, patch 07030105
cpu3: smt 0, core 3, package 0
ioapic0 at mainbus0: apid 4 pa 0xfec00000, version 21, 24 pins
ioapic1 at mainbus0: apid 5 pa 0xfec20000, version 21, 32 pins
acpihpet0 at acpi0: 14318180 Hz
acpiprt0 at acpi0: bus 0 (PCI0)
acpiprt1 at acpi0: bus -1 (PBR4)
acpiprt2 at acpi0: bus 1 (PBR5)
acpiprt3 at acpi0: bus 2 (PBR6)
acpiprt4 at acpi0: bus 3 (PBR7)
acpiprt5 at acpi0: bus -1 (PBR8)
acpicpu0 at acpi0: C2(0@400 io@0x1771), C1(@1 halt!), PSS
acpicpu1 at acpi0: C2(0@400 io@0x1771), C1(@1 halt!), PSS
acpicpu2 at acpi0: C2(0@400 io@0x1771), C1(@1 halt!), PSS
acpicpu3 at acpi0: C2(0@400 io@0x1771), C1(@1 halt!), PSS
acpipci0 at acpi0 PCI0: 0x00000000 0x00000011 0x00000001
acpicmos0 at acpi0
com0 at acpi0 COM1 addr 0x3f8/0x8 irq 4: ns16550a, 16 byte fifo
com0: console
com1 at acpi0 COM2 addr 0x2f8/0x8 irq 3: ns16550a, 16 byte fifo
amdgpio0 at acpi0 GPIO uid 0 addr 0xfed81500/0x300 irq 7, 184 pins
"PRP0001" at acpi0 not configured
"PRP0001" at acpi0 not configured
"PRP0001" at acpi0 not configured
"PRP0001" at acpi0 not configured
"PRP0001" at acpi0 not configured
"PRP0001" at acpi0 not configured
"BOOT0000" at acpi0 not configured
acpitz0 at acpi0
acpitz0: critical temperature is 115 degC
cpu0: 998 MHz: speeds: 1000 800 600 MHz
pci0 at mainbus0 bus 0
pchb0 at pci0 dev 0 function 0 "AMD 16h Root Complex" rev 0x00
vendor "AMD", unknown product 0x1567 (class system subclass IOMMU, rev 0x00) at pci0 dev 0 function 2 not configured
pchb1 at pci0 dev 2 function 0 "AMD 16h Host" rev 0x00
ppb0 at pci0 dev 2 function 2 "AMD 16h PCIE" rev 0x00: msi
pci1 at ppb0 bus 1
em0 at pci1 dev 0 function 0 "Intel I211" rev 0x03: msi, address 00:0d:b9:41:7e:48
ppb1 at pci0 dev 2 function 3 "AMD 16h PCIE" rev 0x00: msi
pci2 at ppb1 bus 2
em1 at pci2 dev 0 function 0 "Intel I211" rev 0x03: msi, address 00:0d:b9:41:7e:49
ppb2 at pci0 dev 2 function 4 "AMD 16h PCIE" rev 0x00: msi
pci3 at ppb2 bus 3
em2 at pci3 dev 0 function 0 "Intel I211" rev 0x03: msi, address 00:0d:b9:41:7e:4a
ccp0 at pci0 dev 8 function 0 "AMD 16h Crypto" rev 0x00
xhci0 at pci0 dev 16 function 0 "AMD Bolton xHCI" rev 0x11: msix, xHCI 1.0
usb0 at xhci0: USB revision 3.0
uhub0 at usb0 configuration 1 interface 0 "AMD xHCI root hub" rev 3.00/1.00 addr 1
ahci0 at pci0 dev 17 function 0 "AMD Hudson-2 SATA" rev 0x40: apic 4 int 19, AHCI 1.3
ahci0: port 0: 3.0Gb/s
scsibus1 at ahci0: 32 targets
sd0 at scsibus1 targ 0 lun 0: <ATA, OCZ-NOCTI, 2.25> naa.5e83a97e555f7072
sd0: 57241MB, 512 bytes/sector, 117231408 sectors, thin
ehci0 at pci0 dev 19 function 0 "AMD Hudson-2 USB2" rev 0x39: apic 4 int 18
usb1 at ehci0: USB revision 2.0
uhub1 at usb1 configuration 1 interface 0 "AMD EHCI root hub" rev 2.00/1.00 addr 1
piixpm0 at pci0 dev 20 function 0 "AMD Hudson-2 SMBus" rev 0x42: SMI
iic0 at piixpm0
iic1 at piixpm0
iic1: addr 0x4c 3e=00 48=00 4a=00 4e=00 fc=00 fe=00 words 00=ffff 01=ffff 02=ffff 03=ffff 04=ffff 05=ffff 06=ffff 07=ffff
pcib0 at pci0 dev 20 function 3 "AMD Hudson-2 LPC" rev 0x11
sdhc0 at pci0 dev 20 function 7 "AMD Bolton SD/MMC" rev 0x01: apic 4 int 16
sdhc0: SDHC 2.00, 50 MHz base clock
sdmmc0 at sdhc0: 4-bit, sd high-speed, mmc high-speed, dma
pchb2 at pci0 dev 24 function 0 "AMD 16h Link Cfg" rev 0x00
pchb3 at pci0 dev 24 function 1 "AMD 16h Address Map" rev 0x00
pchb4 at pci0 dev 24 function 2 "AMD 16h DRAM Cfg" rev 0x00
km0 at pci0 dev 24 function 3 "AMD 16h Misc Cfg" rev 0x00
pchb5 at pci0 dev 24 function 4 "AMD 16h CPU Power" rev 0x00
pchb6 at pci0 dev 24 function 5 "AMD 16h Misc Cfg" rev 0x00
isa0 at pcib0
isadma0 at isa0
com2 at isa0 port 0x3e8/8 irq 5: ns16550a, 16 byte fifo
pcppi0 at isa0 port 0x61
spkr0 at pcppi0
lpt0 at isa0 port 0x378/4 irq 7
intr_establish: pic ioapic0 pin 7: can't share type 3 with 2
wbsio0 at isa0 port 0x2e/2: NCT5104D rev 0x52
vmm0 at mainbus0: SVM/RVI
uhub2 at uhub1 port 1 configuration 1 interface 0 "Advanced Micro Devices Hub" rev 2.00/0.18 addr 2
vscsi0 at root
scsibus2 at vscsi0: 256 targets
softraid0 at root
scsibus3 at softraid0: 256 targets
root on sd0a (af73f066650bc6b9.a) swap on sd0b dump on sd0b

> > Whilst it fixes your machine, how confident can we be that this is harmless on
> > others?
> > 
> > It's perfectly valid to have no graphics hardware at all and run entirely from
> > a serial console, so this could plausibly break machines that are currently
> > working just fine.
> > 
> 
> Well, here my assumption that on amd64, both the VGA legacy memory region
> and I/O ports is still reserved and not used.

if my reading is correct then I think that is ok in this case (but I'm
not 100%) ..

boot> machine mem
Region 0: type 1 at 0x0 for 639KB
Region 1: type 2 at 0x9fc00 for 1KB
Region 2: type 2 at 0xf0000 for 64KB
Region 3: type 1 at 0x100000 for 2078296KB
Region 4: type 2 at 0x7ee96000 for 17832KB
Region 5: type 2 at 0xf8000000 for 65536KB
Region 6: type 2 at 0xfec10000 for 4KB
Region 7: type 2 at 0xfed40000 for 20KB
Low ram: 639KB  High ram: 2078296KB
Total free memory: 2078935KB

> This machine has such region reserved, but you raised a good question: can
> it be reused in the future for something else? My bet here that it will be
> reserved for compatiblity, and this is quite small memory to be reused
> anywere these days.
> 
> I only can think only about a check that goes by bios_memmap and checks that
> this memory is actually reserved (it's true on this), but I have no idea how
> to check that it isn't used for anything other that trivial BIOS_MAP_RES.