[PATCH 1/2] m68k: sun3: register RAM with memblock and set the low pfn limits

[Daniel Palmer <daniel@0x0f.com>]

The sun3 memory init never talked to memblock, so paging_init() and the
first slab allocation found no memory at all:

 * register physical RAM with memblock_add() and reserve the kernel
   image (and embedded initramfs) below memory_start.  The generic
   m68k_setup_node() no longer does this, and sun3's paging_init()
   allocates its page tables straight out of memblock, so without it
   memblock is empty and paging_init() panics;

 * memblock_set_bottom_up(true): paging_init() runs while only the low
   RAM the PROM handed us is mapped, so its page-table allocations must
   come from just above the kernel rather than the unmapped top of RAM;

 * set min_low_pfn/max_low_pfn: memblock_free_all() clamps the pages it
   releases into the buddy allocator to [min_low_pfn, max_low_pfn); with
   them left 0 the whole of RAM stayed reserved and the first slab
   allocation BUG'd.

Assisted-by: Claude:claude-fable-5.1
Signed-off-by: Daniel Palmer <daniel@0x0f.com>
---
 arch/m68k/sun3/config.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/m68k/sun3/config.c b/arch/m68k/sun3/config.c
index cd8af809e0ca..cb4e19b95a1b 100644
--- a/arch/m68k/sun3/config.c
+++ b/arch/m68k/sun3/config.c
@@ -118,6 +118,30 @@ static void __init sun3_bootmem_alloc(unsigned long memory_start,
 	high_memory = (void *)memory_end;
 	availmem = memory_start;
 
+	/*
+	 * memblock_free_all() clamps the pages it releases into the buddy
+	 * allocator to [min_low_pfn, max_low_pfn); without these set the
+	 * whole of RAM stays reserved and the first slab allocation fails.
+	 */
+	min_low_pfn = __pa(memory_start) >> PAGE_SHIFT;
+	max_low_pfn = max_pfn;
+
+	/*
+	 * Register physical RAM with memblock and reserve the kernel image
+	 * (and the embedded initramfs) below memory_start.  The generic
+	 * m68k_setup_node() no longer does this, and sun3's paging_init()
+	 * allocates its page tables straight out of memblock, so without
+	 * this memblock is empty and paging_init() panics.
+	 */
+	memblock_add(0, __pa(memory_end));
+	memblock_reserve(0, __pa(memory_start));
+	/*
+	 * paging_init() runs while only the low RAM the PROM handed us is
+	 * mapped, so its page-table allocations must come from just above
+	 * the kernel (bottom-up) rather than the unmapped top of RAM.
+	 */
+	memblock_set_bottom_up(true);
+
 	m68k_setup_node(0);
 }
 
-- 
2.55.0