powerpc: use mm zones more sensibly

Powerpc has somewhat odd usage where ZONE_DMA is used for all memory on
common 64-bit configfs, and ZONE_DMA32 is used for 31-bit schemes.

Move to a scheme closer to what other architectures use (and I dare to
say the intent of the system):

 - ZONE_DMA: optionally for memory < 31-bit (64-bit embedded only)
 - ZONE_NORMAL: everything addressable by the kernel
 - ZONE_HIGHMEM: memory > 32-bit for 32-bit kernels

Also provide information on how ZONE_DMA is used by defining
ARCH_ZONE_DMA_BITS.

Contains various fixes from Benjamin Herrenschmidt.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 17 insertions, 30 deletions

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 065c37d54b49..20394e52fe27 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -246,35 +246,19 @@ static int __init mark_nonram_nosave(void)
 }
 #endif
 
-static bool zone_limits_final;
-
 /*
- * The memory zones past TOP_ZONE are managed by generic mm code.
- * These should be set to zero since that's what every other
- * architecture does.
+ * Zones usage:
+ *
+ * We setup ZONE_DMA to be 31-bits on all platforms and ZONE_NORMAL to be
+ * everything else. GFP_DMA32 page allocations automatically fall back to
+ * ZONE_DMA.
+ *
+ * By using 31-bit unconditionally, we can exploit ARCH_ZONE_DMA_BITS to
+ * inform the generic DMA mapping code.  32-bit only devices (if not handled
+ * by an IOMMU anyway) will take a first dip into ZONE_NORMAL and get
+ * otherwise served by ZONE_DMA.
  */
-static unsigned long max_zone_pfns[MAX_NR_ZONES] = {
-	[0            ... TOP_ZONE        ] = ~0UL,
-	[TOP_ZONE + 1 ... MAX_NR_ZONES - 1] = 0
-};
-
-/*
- * Restrict the specified zone and all more restrictive zones
- * to be below the specified pfn.  May not be called after
- * paging_init().
- */
-void __init limit_zone_pfn(enum zone_type zone, unsigned long pfn_limit)
-{
-	int i;
-
-	if (WARN_ON(zone_limits_final))
-		return;
-
-	for (i = zone; i >= 0; i--) {
-		if (max_zone_pfns[i] > pfn_limit)
-			max_zone_pfns[i] = pfn_limit;
-	}
-}
+static unsigned long max_zone_pfns[MAX_NR_ZONES];
 
 /*
  * Find the least restrictive zone that is entirely below the
@@ -324,11 +308,14 @@ void __init paging_init(void)
 	printk(KERN_DEBUG "Memory hole size: %ldMB\n",
 	       (long int)((top_of_ram - total_ram) >> 20));
 
+#ifdef CONFIG_ZONE_DMA
+	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn, 0x7fffffffUL >> PAGE_SHIFT);
+#endif
+	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
 #ifdef CONFIG_HIGHMEM
-	limit_zone_pfn(ZONE_NORMAL, lowmem_end_addr >> PAGE_SHIFT);
+	max_zone_pfns[ZONE_HIGHMEM] = max_pfn;
 #endif
-	limit_zone_pfn(TOP_ZONE, top_of_ram >> PAGE_SHIFT);
-	zone_limits_final = true;
+
 	free_area_init_nodes(max_zone_pfns);
 
 	mark_nonram_nosave();