Re: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper

[Hiroshi Doyu <hdoyu@xxxxxxxxxx>]

From: Hiroshi DOYU <hdoyu@xxxxxxxxxx>
Subject: Re: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper
Date: Wed, 07 Mar 2012 08:37:06 +0200 (EET)
Message-ID: <20120307.083706.2087121294965856946.hdoyu@xxxxxxxxxx>

> From: Hiroshi DOYU <hdoyu@xxxxxxxxxx>
> Subject: Re: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper
> Date: Wed, 07 Mar 2012 08:09:52 +0200 (EET)
> Message-ID: <20120307.080952.2152478004740487196.hdoyu@xxxxxxxxxx>
> 
> > From: Krishna Reddy <vdumpa@xxxxxxxxxx>
> > Subject: RE: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper
> > Date: Tue, 6 Mar 2012 23:48:42 +0100
> > Message-ID: <401E54CE964CD94BAE1EB4A729C7087E37970113FE@xxxxxxxxxxxxxxxxxxx>
> > 
> > > > > +struct dma_iommu_mapping *
> > > > > +arm_iommu_create_mapping(struct bus_type *bus, dma_addr_t base, size_t size,
> > > > > +                        int order)
> > > > > +{
> > > > > +       unsigned int count = (size >> PAGE_SHIFT) - order;
> > > > > +       unsigned int bitmap_size = BITS_TO_LONGS(count) * sizeof(long);
> > > 
> > > The count calculation doesn't seem correct. "order" is log2 number and
> > >  size >> PAGE_SHIFT is number of pages. 
> > > 
> > > If size is passed as 64*4096(256KB) and order is 6(allocation granularity is 2^6 pages=256KB),
> > >  just 1 bit is enough to manage allocations.  So it should be 4 bytes or one long.
> > 
> > Good catch!
> > 
> > > But the calculation gives count = 64 - 6 = 58 and 
> > > Bitmap_size gets set to (58/(4*8)) * 4 = 8 bytes, which is incorrect.
> > 
> > "order" isn't the order of size passed, which is minimal *page*
> > allocation order which client decides whatever, just in case.
> > 
> > > It should be as follows.
> > > unsigned int count = 1 << get_order(size) - order;
> 
> To be precise, as below?
> 
>  unsigned int count = 1 << (get_order(size) - order);

This could be:

>From fd40740ef4bc4a3924fe1188ea6dd785be0fe859 Mon Sep 17 00:00:00 2001
From: Hiroshi DOYU <hdoyu@xxxxxxxxxx>
Date: Wed, 7 Mar 2012 08:14:38 +0200
Subject: [PATCH 1/1] dma-mapping: Fix count calculation of iova space

Fix count calculation of iova space.
Pointed by Krishna Reddy <vdumpa@xxxxxxxxxx>

Signed-off-by: Hiroshi DOYU <hdoyu@xxxxxxxxxx>
---
 arch/arm/mm/dma-mapping.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 6c2f104..56f0af5 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1483,11 +1483,18 @@ struct dma_iommu_mapping *
 arm_iommu_create_mapping(struct bus_type *bus, dma_addr_t base, size_t size,
 			 int order)
 {
-	unsigned int count = (size >> PAGE_SHIFT) - order;
-	unsigned int bitmap_size = BITS_TO_LONGS(count) * sizeof(long);
+	unsigned int n, count;
+	unsigned int bitmap_size;
 	struct dma_iommu_mapping *mapping;
 	int err = -ENOMEM;
 
+	n = get_order(size);
+	if (n < order)
+		return ERR_PTR(-EINVAL);
+
+	count = 1 << (n - order);
+	bitmap_size = BITS_TO_LONGS(count) * sizeof(long);
+
 	mapping = kzalloc(sizeof(struct dma_iommu_mapping), GFP_KERNEL);
 	if (!mapping)
 		goto err;
-- 
1.7.5.4
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