The memory layout of the PowerNV machine is defined as :

  #define KERNEL_LOAD_BASE	((void *)0x20000000)
  #define KERNEL_LOAD_SIZE	0x08000000

  #define INITRAMFS_LOAD_BASE	KERNEL_LOAD_BASE + KERNEL_LOAD_SIZE
  #define INITRAMFS_LOAD_SIZE	0x08000000

  #define SKIBOOT_BASE		0x30000000
  #define SKIBOOT_SIZE		0x01c10000

  #define CPU_STACKS_BASE	(SKIBOOT_BASE + SKIBOOT_SIZE)
  #define STACK_SHIFT		15
  #define STACK_SIZE		(1 << STACK_SHIFT)

The overall size of the CPU stacks is (max PIR + 1) * 32K and the
machine easily reaches 800MB of minimum required RAM.

Any value below will result in a skiboot crash :

    [    0.034949905,3] MEM: Partial overlap detected between regions:
    [    0.034959039,3] MEM: ibm,firmware-stacks [0x31c10000-0x3a450000] (new)
    [    0.034968576,3] MEM: ibm,firmware-allocs-memory@0 [0x31c10000-0x38400000]
    [    0.034980367,3] Out of memory adding skiboot reserved areas
    [    0.035074945,3] ***********************************************
    [    0.035093627,3] < assert failed at core/mem_region.c:1129 >
    [    0.035104247,3]     .
    [    0.035108025,3]      .
    [    0.035111651,3]       .
    [    0.035115231,3]         OO__)
    [    0.035119198,3]        <"__/
    [    0.035122980,3]         ^ ^

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20210129111719.790692-1-clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>