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

[Matt Turner <mattst88@gmail.com>]

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>