From: Mark Kettenis Subject: Re: sys/amd64: fallback to VGA text mode on headless systems To: Kirill A. Korinsky Cc: tech@openbsd.org Date: Sun, 08 Feb 2026 18:34:50 +0100 > Date: Fri, 06 Feb 2026 18:39:03 +0100 > From: Kirill A. Korinsky > > On Fri, 30 Jan 2026 23:20:55 +0100, > Kirill A. Korinsky wrote: > > > > On Fri, 30 Jan 2026 23:05:37 +0100, > > Mark Kettenis wrote: > > > > > > > Date: Fri, 30 Jan 2026 20:39:34 +0100 > > > > From: Kirill A. Korinsky > > > > > > > > On Tue, 27 Jan 2026 15:23:55 +0100, > > > > Kirill A. Korinsky wrote: > > > > > > > > > > On Tue, 27 Jan 2026 13:18:50 +0100, > > > > > Crystal Kolipe wrote: > > > > > > > > > > > > On Tue, Jan 27, 2026 at 11:31:50AM +0000, Stuart Henderson wrote: > > > > > > > On 2026/01/27 12:05, Kirill A. Korinsky wrote: > > > > > > > > On Tue, 27 Jan 2026 10:21:02 +0100, > > > > > > > > Crystal Kolipe wrote: > > > > > > > > > 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 > > > > > > > > > > > > The VGA memory space is certainly marked as reserved. > > > > > > > > > > > > But 'reserved' doesn't mean that writing arbitrary values to those addresses > > > > > > is harmless. > > > > > > > > > > > > > > > > But for compatiblity it should stay reserved for VGA, and to reuse it for > > > > > something else BIOS should have two code paths: when VGA is avaialbel and > > > > > when it isn't. > > > > > > > > > > This is quite small region and introduce two code path seems strange. > > > > > > > > > > But, again, here many assumptions. > > > > > > > > > > > > > Here the second attempt. This time it is looks safer. > > > > > > > > Idea to scan PCI bus to find some VGA adapter and use it as primamary. > > > > > > > > More or less similar with Loongson's approach. > > > > > > > > It allows to boot this machine without serial and amdgpu and dmesg has: > > > > > > > > ~ $ grep vga /var/run/dmesg.boot > > > > vga1 at pci13 dev 0 function 0 "ATI Raphael" rev 0xc9 > > > > wsdisplay0 at vga1 mux 1: console (80x25, vt100 emulation) > > > > ~ $ > > > > > > > > which is expected. > > > > > > > > Thoughts? Tests? OKs? > > > > > > What about my suggestion to have a dummy framebuffer? > > > > > > > I had tried, but I wasn't able make something that works. > > > > Or better to say all my attemt leads to that machine still hungs. > > > > Here hard part: this is remote machine, I haven't got access to serial > > console on it, I can only boot it, or boot in "rescue mode" (Linux) or as > > to attach KVM. > > > > ... and without the way to debug I can't figure out why and where it hangs. > > > > Shall I drop this diff ? Does the diff below work for you? Index: arch/amd64/amd64/efifb.c =================================================================== RCS file: /cvs/src/sys/arch/amd64/amd64/efifb.c,v diff -u -p -r1.34 efifb.c --- arch/amd64/amd64/efifb.c 15 Jul 2022 17:57:25 -0000 1.34 +++ arch/amd64/amd64/efifb.c 8 Feb 2026 17:33:13 -0000 @@ -578,6 +578,33 @@ cb_find_fb(paddr_t addr) return NULL; } +int +efifb_dummy_cnattach(void) +{ + const int width = 1024; + const int height = 768; + struct pglist mlist; + int error; + + memset(&efifb_console, 0, sizeof(efifb_console)); + efifb_console.cb_table_fb.x_resolution = width; + efifb_console.cb_table_fb.y_resolution = height; + + TAILQ_INIT(&mlist); + error = uvm_pglistalloc(width * height, 0, -1, PAGE_SIZE, 0, + &mlist, 1, UVM_PLA_WAITOK); + if (error) + return (-1); + + efifb_console.paddr = VM_PAGE_TO_PHYS(TAILQ_FIRST(&mlist)); + efifb_console.depth = 8; + efifb_console.psize = width * height; + + efifb_cnattach_common(); + + return (0); +} + psize_t efifb_stolen(void) { Index: arch/amd64/amd64/wscons_machdep.c =================================================================== RCS file: /cvs/src/sys/arch/amd64/amd64/wscons_machdep.c,v diff -u -p -r1.14 wscons_machdep.c --- arch/amd64/amd64/wscons_machdep.c 14 Oct 2017 04:44:43 -0000 1.14 +++ arch/amd64/amd64/wscons_machdep.c 8 Feb 2026 17:33:13 -0000 @@ -152,6 +152,10 @@ wscn_video_init(void) if (pcdisplay_cnattach(X86_BUS_SPACE_IO, X86_BUS_SPACE_MEM) == 0) return (0); #endif +#if (NEFIFB > 0) + if (efifb_dummy_cnattach() == 0) + return (0); +#endif return (-1); } Index: arch/amd64/include/efifbvar.h =================================================================== RCS file: /cvs/src/sys/arch/amd64/include/efifbvar.h,v diff -u -p -r1.10 efifbvar.h --- arch/amd64/include/efifbvar.h 4 May 2019 11:34:47 -0000 1.10 +++ arch/amd64/include/efifbvar.h 8 Feb 2026 17:33:13 -0000 @@ -34,6 +34,7 @@ void efifb_reattach(void); int efifb_cb_found(void); int efifb_cb_cnattach(void); +int efifb_dummy_cnattach(void); psize_t efifb_stolen(void);