powerpc/fsl-pci: Limit ZONE_DMA32 to 2GiB on 64-bit platforms

FSL PCI cannot directly address the whole lower 4 GiB due to
conflicts with PCICSRBAR and outbound windows.  By the time
max_direct_dma_addr is set to the precise limit, it will be too late to
alter the zone limits, but we should always have at least 2 GiB mapped
(unless RAM is smaller than that).
Signed-off-by: Scott Wood <scottwood@freescale.com>
Cc: Shaohui Xie <Shaohui.Xie@freescale.com>

arch/powerpc/platforms/85xx/corenet_generic.c

@@ -20,6 +20,7 @@
 #include <asm/time.h>
 #include <asm/machdep.h>
 #include <asm/pci-bridge.h>
+#include <asm/pgtable.h>
 #include <asm/ppc-pci.h>
 #include <mm/mmu_decl.h>
 #include <asm/prom.h>
@@ -67,6 +68,16 @@ void __init corenet_gen_setup_arch(void)
 
 	swiotlb_detect_4g();
 
+#if defined(CONFIG_FSL_PCI) && defined(CONFIG_ZONE_DMA32)
+	/*
+	 * Inbound windows don't cover the full lower 4 GiB
+	 * due to conflicts with PCICSRBAR and outbound windows,
+	 * so limit the DMA32 zone to 2 GiB, to allow consistent
+	 * allocations to succeed.
+	 */
+	limit_zone_pfn(ZONE_DMA32, 1UL << (31 - PAGE_SHIFT));
+#endif
+
 	pr_info("%s board\n", ppc_md.name);
 
 	mpc85xx_qe_init();

arch/powerpc/platforms/85xx/qemu_e500.c

@@ -18,6 +18,7 @@
 #include <linux/kernel.h>
 #include <linux/of_fdt.h>
 #include <asm/machdep.h>
+#include <asm/pgtable.h>
 #include <asm/time.h>
 #include <asm/udbg.h>
 #include <asm/mpic.h>
@@ -44,6 +45,15 @@ static void __init qemu_e500_setup_arch(void)
 
 	fsl_pci_assign_primary();
 	swiotlb_detect_4g();
+#if defined(CONFIG_FSL_PCI) && defined(CONFIG_ZONE_DMA32)
+	/*
+	 * Inbound windows don't cover the full lower 4 GiB
+	 * due to conflicts with PCICSRBAR and outbound windows,
+	 * so limit the DMA32 zone to 2 GiB, to allow consistent
+	 * allocations to succeed.
+	 */
+	limit_zone_pfn(ZONE_DMA32, 1UL << (31 - PAGE_SHIFT));
+#endif
 	mpc85xx_smp_init();
 }