[PATCH 2.4.30-pre3] x86_64: pci_alloc_consistent() match 2.6 implementation

[Matt Domsch <Matt_Domsch@dell.com>]

For review and comment.

On x86_64 systems with no IOMMU and with >4GB RAM (in fact, whenever
there are any pages mapped above 4GB), pci_alloc_consistent() falls
back to using ZONE_DMA for all allocations, even if the device's
dma_mask could have supported using memory from other zones.  Problems
can be seen when other ZONE_DMA users (SWIOTLB, scsi_malloc()) consume
all of ZONE_DMA, leaving none left for pci_alloc_consistent() use.

Patch below makes pci_alloc_consistent() for the nommu case (EM64T
processors) match the 2.6 implementation of dma_alloc_coherent(), with
the exception that this continues to use GFP_ATOMIC.

Signed-off-by: Matt Domsch <Matt_Domsch@dell.com>

Thanks,
Matt

-- 
Matt Domsch
Software Architect
Dell Linux Solutions linux.dell.com & www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com

--- linux-2.4/arch/x86_64/kernel/pci-nommu.c	Fri Feb 25 13:01:44 2005
+++ linux-2.4/arch/x86_64/kernel/pci-nommu.c	Fri Feb 25 06:56:55 2005
@@ -13,18 +13,28 @@ void *pci_alloc_consistent(struct pci_de
 			   dma_addr_t *dma_handle)
 {
 	void *ret;
+	u64 mask;
+	int order = get_order(size);
 	int gfp = GFP_ATOMIC;
-	
-	if (hwdev == NULL ||
-	    end_pfn > (hwdev->dma_mask>>PAGE_SHIFT) ||  /* XXX */
-	    (u32)hwdev->dma_mask < 0xffffffff)
-		gfp |= GFP_DMA;
-	ret = (void *)__get_free_pages(gfp, get_order(size));
 
-	if (ret != NULL) {
-		memset(ret, 0, size);
+	if (hwdev)
+		mask = hwdev->dma_mask;
+	else
+		mask = 0xffffffffULL;
+
+	for (;;) {
+		ret = (void *)__get_free_pages(gfp, order);
+		if (ret == NULL)
+			return NULL;
 		*dma_handle = virt_to_bus(ret);
+		if ((*dma_handle & ~mask) == 0)
+			break;
+		free_pages((unsigned long)ret, order);
+		if (gfp & GFP_DMA)
+			return NULL;
+		gfp |= GFP_DMA;
 	}
+	memset(ret, 0, size);
 	return ret;
 }