linux-kernel - Re: [PATCH] arm:swiotlb:keep disabled in default configuration

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Date:	Thu, 23 Jun 2016 17:00:20 +0100 (BST)
From:	Stefano Stabellini <sstabellini@...nel.org>
To:	konrad@...nok.org
cc:	manjeet.p@...sung.com, pankaj.m@...sung.com, ajeet.y@...sung.com,
	r.thapliyal@...sung.com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux@....linux.org.uk,
	sstabellini@...nel.org
Subject: Re: [PATCH] arm:swiotlb:keep disabled in default configuration

On Thu, 23 Jun 2016, Stefano Stabellini wrote:
> On Jun 23, 2016 8:27 AM, "Manjeet Pawar" <manjeet.p@...sung.com> wrote:
> >
> > From: Rohit Thapliyal <r.thapliyal@...sung.com>
> >
> > swiotlb implementation not required to be enabled in arm and
> > disabling it reduces uImage size by 16KB.
> >
> 
> How so? There are no DMA operations on ARM?

Xen actively uses the swiotlb on ARM, see

arch/arm64/include/asm/dma-mapping.h:get_dma_ops
arch/arm/xen/mm.c:xen_swiotlb_dma_ops


> > Signed-off-by: Rohit Thapliyal <r.thapliyal@...sung.com>
> > Signed-off-by: Ajeet Kumar Yadav <ajeet.y@...sung.com>
> > ---
> >  arch/arm/Kconfig |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index 90542db..ae65f29 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -1754,7 +1754,7 @@ config SECCOMP
> >           defined by each seccomp mode.
> >
> >  config SWIOTLB
> > -       def_bool y
> > +       def_bool n
> >
> >  config IOMMU_HELPER
> >         def_bool SWIOTLB
> > --
> > 1.7.9.5
> >
>