linux-kernel - Re: [PATCH -mm] SWIOTLB: use iommu_is_span

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Date:	Wed, 2 Apr 2008 14:19:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	linux-kernel@...r.kernel.org, tomof@....org,
	fujita.tomonori@....ntt.co.jp, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, tony.luck@...el.com
Subject: Re: [PATCH -mm] SWIOTLB: use iommu_is_span_boundary helper function

On Thu,  3 Apr 2008 06:02:35 +0900
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:

> iommu_is_span_boundary in lib/iommu-helper.c was exported for PARISC
> IOMMUs (commit 3715863aa142c4f4c5208f5f3e5e9bac06006d2f). SWIOTLB can
> use it instead of the homegrown function.
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  arch/ia64/Kconfig |    5 ++++-
>  arch/x86/Kconfig  |    5 ++---
>  lib/swiotlb.c     |   14 +++-----------
>  3 files changed, 9 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
> index 53b8410..6840a13 100644
> --- a/arch/ia64/Kconfig
> +++ b/arch/ia64/Kconfig
> @@ -47,6 +47,9 @@ config MMU
>  config SWIOTLB
>         bool
>  
> +config IOMMU_HELPER
> +       bool
> +
>  config GENERIC_LOCKBREAK
>  	bool
>  	default y
> @@ -624,7 +627,7 @@ config IRQ_PER_CPU
>  	default y
>  
>  config IOMMU_HELPER
> -	def_bool (IA64_HP_ZX1 || IA64_HP_ZX1_SWIOTLB || IA64_GENERIC)
> +	def_bool (IA64_HP_ZX1 || IA64_HP_ZX1_SWIOTLB || IA64_GENERIC || SWIOTLB)
>  
>  source "arch/ia64/hp/sim/Kconfig"
>  
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 1f44517..e6c01c2 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -502,9 +502,6 @@ config CALGARY_IOMMU_ENABLED_BY_DEFAULT
>  	  Calgary anyway, pass 'iommu=calgary' on the kernel command line.
>  	  If unsure, say Y.
>  
> -config IOMMU_HELPER
> -	def_bool (CALGARY_IOMMU || GART_IOMMU)
> -
>  # need this always selected by IOMMU for the VIA workaround
>  config SWIOTLB
>  	bool
> @@ -515,6 +512,8 @@ config SWIOTLB
>  	  access 32-bits of memory can be used on systems with more than
>  	  3 GB of memory. If unsure, say Y.
>  
> +config IOMMU_HELPER
> +	def_bool (CALGARY_IOMMU || GART_IOMMU || SWIOTLB)
>  
>  config NR_CPUS
>  	int "Maximum number of CPUs (2-255)"
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 62c9a18..b50c7e0 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -31,6 +31,7 @@
>  
>  #include <linux/init.h>
>  #include <linux/bootmem.h>
> +#include <linux/iommu-helper.h>
>  
>  #define OFFSET(val,align) ((unsigned long)	\
>  	                   ( (val) & ( (align) - 1)))
> @@ -282,15 +283,6 @@ address_needs_mapping(struct device *hwdev, dma_addr_t addr)
>  	return (addr & ~mask) != 0;
>  }
>  
> -static inline unsigned int is_span_boundary(unsigned int index,
> -					    unsigned int nslots,
> -					    unsigned long offset_slots,
> -					    unsigned long max_slots)
> -{
> -	unsigned long offset = (offset_slots + index) & (max_slots - 1);
> -	return offset + nslots > max_slots;
> -}
> -
>  /*
>   * Allocates bounce buffer and returns its kernel virtual address.
>   */
> @@ -338,8 +330,8 @@ map_single(struct device *hwdev, char *buffer, size_t size, int dir)
>  	wrap = index;
>  
>  	do {
> -		while (is_span_boundary(index, nslots, offset_slots,
> -				max_slots)) {
> +		while (iommu_is_span_boundary(index, nslots, offset_slots,
> +					      max_slots)) {
>  			index += stride;
>  			if (index >= io_tlb_nslabs)
>  				index = 0;

Fair enough.

It's confusing that iommu_is_span_boundary() uses index, nr, shift and
boundary_size whereas is_span_boundary() used index, nslots, offset_slots,
and max_slots.  Which one was most accurate, clearer, etc?

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