From: Olaf Hering <olh@suse.de>
Subject: new prom=nodisplay option to avoid crash in firmware on B50
Patch-mainline: not yet

add prom=nodisplay
avoid crash in firmware on IBM B50 when OF stdout is on serial.

 0 > boot scsi/sd@4:1,yaboot |
yaboot starting: loaded at 00200000 00222530 (0/0/00c1a078; sp: 00efffd0)
brokenfirmware did not claim executable memory, fixed it myself
Config file 'yaboot.cnf' read, 213 bytes

Welcome to yaboot version 10.1.22-r945.SuSE
booted from '/pci@80000000/scsi@10/sd@4:1,yaboot'
Enter "help" to get some basic usage information
boot:
* linux
boot: linux 3
Please wait, loading kernel...
Allocated 00600000 bytes for executable @ 02000000
   Elf32 kernel loaded...
Loading ramdisk...
ramdisk loaded 0030e057 @ 04100000
OF stdout device is: /pci@80000000/isa@b/serial@i3f8
command line: root=/dev/system/root  xmon=on sysrq=1 quiet panic=12 3
memory layout at init:   
  memory_limit : 00000000 (16 MB aligned)
  alloc_bottom : 0440f000
  alloc_top    : 30000000
  alloc_top_hi : 40000000
  rmo_top      : 30000000
  ram_top      : 40000000
Looking for displays
found display   : /pci@80000000/display@16, opening ...
Unexpected Firmware Error:
DEFAULT CATCH!, code=fff00300 at   %SRR0: 00c18ccc   %SRR1: 00003030
 ok
 0 > reset-all


---
 arch/powerpc/kernel/prom_init.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -169,6 +169,7 @@ static unsigned long __initdata dt_strin
 
 static unsigned long __initdata prom_initrd_start, prom_initrd_end;
 
+static int __initdata prom_no_display;
 #ifdef CONFIG_PPC64
 static int __initdata prom_iommu_force_on;
 static int __initdata prom_iommu_off;
@@ -596,6 +597,14 @@ static void __init early_cmdline_parse(v
 #endif /* CONFIG_CMDLINE */
 	prom_printf("command line: %s\n", RELOC(prom_cmd_line));
 
+	opt = strstr(RELOC(prom_cmd_line), RELOC("prom="));
+	if (opt) {
+		opt += 5;
+		while (*opt && *opt == ' ')
+			opt++;
+		if (!strncmp(opt, RELOC("nodisplay"), 9))
+			RELOC(prom_no_display) = 1;
+	}
 #ifdef CONFIG_PPC64
 	opt = strstr(RELOC(prom_cmd_line), RELOC("iommu="));
 	if (opt) {
@@ -2570,6 +2579,7 @@ unsigned long __init prom_init(unsigned
 	/* 
 	 * Initialize display devices
 	 */
+	if (RELOC(prom_no_display) == 0)
 	prom_check_displays();
 
 #ifdef CONFIG_PPC64