powerpc: Fix up dma_alloc_coherent() on platforms without cache coherency.

The implementation we just revived has issues, such as using a
Kconfig-defined virtual address area in kernel space that nothing
actually carves out (and thus will overlap whatever is there),
or having some dependencies on being self contained in a single
PTE page which adds unnecessary constraints on the kernel virtual
address space.

This fixes it by using more classic PTE accessors and automatically
locating the area for consistent memory, carving an appropriate hole
in the kernel virtual address space, leaving only the size of that
area as a Kconfig option. It also brings some dma-mask related fixes
from the ARM implementation which was almost identical initially but
grew its own fixes.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

2 files changed, 45 insertions, 67 deletions

diff --git a/arch/powerpc/mm/dma-noncoherent.c b/arch/powerpc/mm/dma-noncoherent.c
index b7dc4c19f58..36692f5c9a7 100644
--- a/arch/powerpc/mm/dma-noncoherent.c
+++ b/arch/powerpc/mm/dma-noncoherent.c
@@ -32,20 +32,21 @@
 
 #include <asm/tlbflush.h>
 
+#include "mmu_decl.h"
+
 /*
  * This address range defaults to a value that is safe for all
  * platforms which currently set CONFIG_NOT_COHERENT_CACHE. It
  * can be further configured for specific applications under
  * the "Advanced Setup" menu. -Matt
  */
-#define CONSISTENT_BASE	(CONFIG_CONSISTENT_START)
-#define CONSISTENT_END	(CONFIG_CONSISTENT_START + CONFIG_CONSISTENT_SIZE)
+#define CONSISTENT_BASE		(IOREMAP_TOP)
+#define CONSISTENT_END 		(CONSISTENT_BASE + CONFIG_CONSISTENT_SIZE)
 #define CONSISTENT_OFFSET(x)	(((unsigned long)(x) - CONSISTENT_BASE) >> PAGE_SHIFT)
 
 /*
  * This is the page table (2MB) covering uncached, DMA consistent allocations
  */
-static pte_t *consistent_pte;
 static DEFINE_SPINLOCK(consistent_lock);
 
 /*
@@ -148,22 +149,38 @@ static struct ppc_vm_region *ppc_vm_region_find(struct ppc_vm_region *head, unsi
  * virtual and bus address for that space.
  */
 void *
-__dma_alloc_coherent(size_t size, dma_addr_t *handle, gfp_t gfp)
+__dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *handle, gfp_t gfp)
 {
 	struct page *page;
 	struct ppc_vm_region *c;
 	unsigned long order;
-	u64 mask = 0x00ffffff, limit; /* ISA default */
+	u64 mask = ISA_DMA_THRESHOLD, limit;
 
-	if (!consistent_pte) {
-		printk(KERN_ERR "%s: not initialised\n", __func__);
-		dump_stack();
-		return NULL;
+	if (dev) {
+		mask = dev->coherent_dma_mask;
+
+		/*
+		 * Sanity check the DMA mask - it must be non-zero, and
+		 * must be able to be satisfied by a DMA allocation.
+		 */
+		if (mask == 0) {
+			dev_warn(dev, "coherent DMA mask is unset\n");
+			goto no_page;
+		}
+
+		if ((~mask) & ISA_DMA_THRESHOLD) {
+			dev_warn(dev, "coherent DMA mask %#llx is smaller "
+				 "than system GFP_DMA mask %#llx\n",
+				 mask, (unsigned long long)ISA_DMA_THRESHOLD);
+			goto no_page;
+		}
 	}
 
+
 	size = PAGE_ALIGN(size);
 	limit = (mask + 1) & ~mask;
-	if ((limit && size >= limit) || size >= (CONSISTENT_END - CONSISTENT_BASE)) {
+	if ((limit && size >= limit) ||
+	    size >= (CONSISTENT_END - CONSISTENT_BASE)) {
 		printk(KERN_WARNING "coherent allocation too big (requested %#x mask %#Lx)\n",
 		       size, mask);
 		return NULL;
@@ -171,6 +188,7 @@ __dma_alloc_coherent(size_t size, dma_addr_t *handle, gfp_t gfp)
 
 	order = get_order(size);
 
+	/* Might be useful if we ever have a real legacy DMA zone... */
 	if (mask != 0xffffffff)
 		gfp |= GFP_DMA;
 
@@ -195,7 +213,6 @@ __dma_alloc_coherent(size_t size, dma_addr_t *handle, gfp_t gfp)
 			    gfp & ~(__GFP_DMA | __GFP_HIGHMEM));
 	if (c) {
 		unsigned long vaddr = c->vm_start;
-		pte_t *pte = consistent_pte + CONSISTENT_OFFSET(vaddr);
 		struct page *end = page + (1 << order);
 
 		split_page(page, order);
@@ -206,13 +223,10 @@ __dma_alloc_coherent(size_t size, dma_addr_t *handle, gfp_t gfp)
 		*handle = page_to_phys(page);
 
 		do {
-			BUG_ON(!pte_none(*pte));
-
 			SetPageReserved(page);
-			set_pte_at(&init_mm, vaddr,
-				   pte, mk_pte(page, pgprot_noncached(PAGE_KERNEL)));
+			map_page(vaddr, page_to_phys(page),
+				 pgprot_noncached(PAGE_KERNEL));
 			page++;
-			pte++;
 			vaddr += PAGE_SIZE;
 		} while (size -= PAGE_SIZE);
 
@@ -241,8 +255,7 @@ void __dma_free_coherent(size_t size, void *vaddr)
 {
 	struct ppc_vm_region *c;
 	unsigned long flags, addr;
-	pte_t *ptep;
-
+	
 	size = PAGE_ALIGN(size);
 
 	spin_lock_irqsave(&consistent_lock, flags);
@@ -258,29 +271,26 @@ void __dma_free_coherent(size_t size, void *vaddr)
 		size = c->vm_end - c->vm_start;
 	}
 
-	ptep = consistent_pte + CONSISTENT_OFFSET(c->vm_start);
 	addr = c->vm_start;
 	do {
-		pte_t pte = ptep_get_and_clear(&init_mm, addr, ptep);
+		pte_t *ptep;
 		unsigned long pfn;
 
-		ptep++;
-		addr += PAGE_SIZE;
-
-		if (!pte_none(pte) && pte_present(pte)) {
-			pfn = pte_pfn(pte);
-
+		ptep = pte_offset_kernel(pmd_offset(pud_offset(pgd_offset_k(addr),
+							       addr),
+						    addr),
+					 addr);
+		if (!pte_none(*ptep) && pte_present(*ptep)) {
+			pfn = pte_pfn(*ptep);
+			pte_clear(&init_mm, addr, ptep);
 			if (pfn_valid(pfn)) {
 				struct page *page = pfn_to_page(pfn);
-				ClearPageReserved(page);
 
+				ClearPageReserved(page);
 				__free_page(page);
-				continue;
 			}
 		}
-
-		printk(KERN_CRIT "%s: bad page in kernel page table\n",
-		       __func__);
+		addr += PAGE_SIZE;
 	} while (size -= PAGE_SIZE);
 
 	flush_tlb_kernel_range(c->vm_start, c->vm_end);
@@ -301,42 +311,6 @@ void __dma_free_coherent(size_t size, void *vaddr)
 EXPORT_SYMBOL(__dma_free_coherent);
 
 /*
- * Initialise the consistent memory allocation.
- */
-static int __init dma_alloc_init(void)
-{
-	pgd_t *pgd;
-	pud_t *pud;
-	pmd_t *pmd;
-	pte_t *pte;
-	int ret = 0;
-
-	do {
-		pgd = pgd_offset(&init_mm, CONSISTENT_BASE);
-		pud = pud_alloc(&init_mm, pgd, CONSISTENT_BASE);
-		pmd = pmd_alloc(&init_mm, pud, CONSISTENT_BASE);
-		if (!pmd) {
-			printk(KERN_ERR "%s: no pmd tables\n", __func__);
-			ret = -ENOMEM;
-			break;
-		}
-
-		pte = pte_alloc_kernel(pmd, CONSISTENT_BASE);
-		if (!pte) {
-			printk(KERN_ERR "%s: no pte tables\n", __func__);
-			ret = -ENOMEM;
-			break;
-		}
-
-		consistent_pte = pte;
-	} while (0);
-
-	return ret;
-}
-
-core_initcall(dma_alloc_init);
-
-/*
  * make an area consistent.
  */
 void __dma_sync(void *vaddr, size_t size, int direction)
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index d3a4e67561f..579382c163a 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -387,6 +387,10 @@ void __init mem_init(void)
 	pr_info("  * 0x%08lx..0x%08lx  : highmem PTEs\n",
 		PKMAP_BASE, PKMAP_ADDR(LAST_PKMAP));
 #endif /* CONFIG_HIGHMEM */
+#ifdef CONFIG_NOT_COHERENT_CACHE
+	pr_info("  * 0x%08lx..0x%08lx  : consistent mem\n",
+		IOREMAP_TOP, IOREMAP_TOP + CONFIG_CONSISTENT_SIZE);
+#endif /* CONFIG_NOT_COHERENT_CACHE */
 	pr_info("  * 0x%08lx..0x%08lx  : early ioremap\n",
 		ioremap_bot, IOREMAP_TOP);
 	pr_info("  * 0x%08lx..0x%08lx  : vmalloc & ioremap\n",