linux-kernel - Re: [PATCH] swiotlb updates for Xen dom0

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Date:	Thu, 2 Apr 2009 15:29:15 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	jeremy@...p.org
Cc:	fujita.tomonori@....ntt.co.jp, x86@...nel.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] swiotlb updates for Xen dom0

On Tue, 31 Mar 2009 15:52:06 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> This series adds Xen support to x86 swiotlb.  This is mostly a matter of
> adding some Xen code into the existing hooks in pci-swiotlb_64.c:
>   - swiotlb_alloc_boot
>   - swiotlb_arch_range_needs_mapping
>   - swiotlb_phys_to_bus/bus_to_phys
> 
> These hooks are conditional on xen_pv_domain(), which compiles to a
> constant 0 when CONFIG_XEN is not enabled (and is a simple variable
> read when it is).
> 
> All the Xen-specific code is in xen-iommu.c.
> 
> This series is just the patches which touch lib/swiotlb.c or
> pci-swiotlb_64.c.  You can see them with more context in:
>    git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git for-linus/xen/dom0/swiotlb
> 
> Thanks,
> 	J
> 
>  arch/x86/kernel/pci-swiotlb_64.c |   31 ++++++++++++++++-
>  arch/x86/xen/Kconfig             |    1 
>  drivers/pci/xen-iommu.c          |   68 ++++++++++++++++++++++++++++++++++++---
>  include/xen/swiotlb.h            |   38 +++++++++++++++++++++
>  lib/swiotlb.c                    |    3 +
>  5 files changed, 133 insertions(+), 8 deletions(-)

This patchset looks ugly.

You add 'if we are Xen, we do A. We do B if not' code into 6 functions
though pic-swiotlb_64.c has only 8 functions. In addition, 5 of 8
functions were added for Xen.

Why can't you have something like arch/x86/xen/pci-swiotlb.c, which
works as arch/x86/kernel/pci-swiotlb_64.c? That should be much
cleaner.
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