linux-kernel - Re: [RFC][PATCH] x86 calgary: add fallback dma

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Message-Id: <20080509081322J.tomof@acm.org>
Date:	Fri, 9 May 2008 08:13:46 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	alexisb@...ibm.com
Cc:	linux-kernel@...r.kernel.org, muli@...ibm.com
Subject: Re: [RFC][PATCH] x86 calgary: add fallback dma_ops]]

On Thu, 08 May 2008 14:40:20 -0700
Alexis Bruemmer <alexisb@...ibm.com> wrote:

> Currently the calgary code can give drivers addresses above 4GB which is
> very bad for hardware that is only 32bit DMA addressable.  This patch
> "teaches" calgary to fallback to the appropriate dma_ops when it
> encounters a device/bus which is not behind the Calgary/CalIOC2.  I
> believe there is a better way to do this and am open for ideas, but for
> now this certainly fixes the badness.

I'm not sure that I correctly understand what you want. You mean that
the Calgary IOMMU code ignores device's dma_mask and gives addresses
above 4GB or the Calgary IOMMU code wrongly handles devices that are
not behind the Calgary?

If you refers to the former problem, other IOMMU implementations do
something like this.


diff --git a/arch/x86/kernel/pci-calgary_64.c b/arch/x86/kernel/pci-calgary_64.c
index e28ec49..2a977bc 100644
--- a/arch/x86/kernel/pci-calgary_64.c
+++ b/arch/x86/kernel/pci-calgary_64.c
@@ -268,21 +268,37 @@ static unsigned long iommu_range_alloc(struct device *dev,
 {
 	unsigned long flags;
 	unsigned long offset;
+	unsigned long limit;
 	unsigned long boundary_size;
+	unsigned long start;
+	unsigned long mask;
 
 	boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
 			      PAGE_SIZE) >> PAGE_SHIFT;
 
 	BUG_ON(npages == 0);
 
+	if (dev->dma_mask)
+		mask = *dev->dma_mask >> PAGE_SHIFT;
+	else
+		mask = 0xfffffffful >> PAGE_SHIFT;
+
+	limit = tbl->it_size;
+	start = tbl->it_hint;
+
+	if (limit > mask) {
+		limit = mask + 1;
+		start = tbl->it_hint & mask;
+	}
+
 	spin_lock_irqsave(&tbl->it_lock, flags);
 
-	offset = iommu_area_alloc(tbl->it_map, tbl->it_size, tbl->it_hint,
+	offset = iommu_area_alloc(tbl->it_map, limit, start,
 				  npages, 0, boundary_size, 0);
 	if (offset == ~0UL) {
 		tbl->chip_ops->tce_cache_blast(tbl);
 
-		offset = iommu_area_alloc(tbl->it_map, tbl->it_size, 0,
+		offset = iommu_area_alloc(tbl->it_map, limit, 0,
 					  npages, 0, boundary_size, 0);
 		if (offset == ~0UL) {
 			printk(KERN_WARNING "Calgary: IOMMU full.\n");
--
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