Re: [PATCH] vgacon: Fall back to the dummy console if mapping VGA memory fails

[Michael Cree <mcree@orcon.net.nz>]

On Thu, Nov 12, 2026 at 09:47:05AM +0100, Magnus Lindholm wrote:
> Hi Matt,
> 
> On Thu, Nov 12, 2026 at 1:30 AM Matt Turner <mattst88@gmail.com> wrote:
> >
> > On Alpha, setup_arch() registers vgacon whenever CONFIG_VGA_CONSOLE is
> > enabled. On Marvel (EV7) systems whose SRM console is serial, no VGA
> > hose is set, so marvel_ioremap() finds no hose for 0xb8000 and returns
> > NULL. vgacon_startup() then probes video memory through that NULL
> > pointer and oopses in console_init():
> >
> >   Unable to handle kernel paging request at virtual address 0000000000000000
> >   pc is at vgacon_startup+0x174/0x910
> >
> > VGA_MAP_MEM() is ioremap() on Alpha and powerpc and can fail. Treat
> > failure like a failed probe and fall back to the dummy console. If a
> > VGA card is present, locate_and_init_vga() still switches to vgacon
> > once PCI is up.
> >
> > Cc: stable@vger.kernel.org
> > Assisted-by: Claude:claude-opus-5-5
> > Signed-off-by: Matt Turner <mattst88@gmail.com>
> > ---
> >  drivers/video/console/vgacon.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> > index e7e6750f1f87..09f7c376b468 100644
> > --- a/drivers/video/console/vgacon.c
> > +++ b/drivers/video/console/vgacon.c
> > @@ -324,6 +324,8 @@ static const char *vgacon_startup(void)
> >         }
> >
> >         vga_vram_base = VGA_MAP_MEM(vga_vram_base, vga_vram_size);
> > +       if (!vga_vram_base)
> > +               goto no_vga;
> >         vga_vram_end = vga_vram_base + vga_vram_size;
> >
> >         /*
> >
> > ---
> > base-commit: fa4ad798f6f681031775266044ba1b0cf3c670bd
> > change-id: 20261111-vgacon-ioremap-null-ad4c7184b807
> >
> > Best regards,
> > --
> > Matt Turner <mattst88@gmail.com>
> >
> >
> 
> Nice fix! this must have been lingering here for a long time?
> Cross-builds passed for generic Alpha, including Marvel. The shared
> vgacon code also compiled successfully for x86-64.

I wonder whether this is the reason why my ES45 would never boot with
an AGP video card.  SRM could bring up the console but I recall the
kernel crashed early on.  In contrast, it boots fine with a PCI radeon
card. Not sure if I am going to get a chance to test it out in the
near future though ...

Cheers,
Michael.