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

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Message-id: <762265370.17291466751484096.JavaMail.weblogic@epmlwas08b>
Date:	Fri, 24 Jun 2016 06:58:05 +0000 (GMT)
From:	Manjeet Pawar <manjeet.p@...sung.com>
To:	Stefano Stabellini <sstabellini@...nel.org>,
	"konrad@...nok.org" <konrad@...nok.org>
Cc:	PANKAJ MISHRA <pankaj.m@...sung.com>,
	AJEET YADAV <ajeet.y@...sung.com>,
	Rohit Thapliyal <r.thapliyal@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>
Subject: Re: Re: [PATCH] arm:swiotlb:keep disabled in default configuration

> > On Jun 23, 2016 8:27 AM, "Manjeet Pawar" wrote:
>> >
>> > From: Rohit Thapliyal 
>> >
>> > 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

If XEN is enabled, it shall eventually enable SWIOTLB through SWIOTLB_XEN. So, there is no need to keep it enabled otherwise.


------- Original Message -------
Sender : Stefano Stabellini<sstabellini@...nel.org>
Date : Jun 24, 2016 01:00 (GMT+09:00)
Title : 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" wrote:
> >
> > From: Rohit Thapliyal 
> >
> > 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 
> > Signed-off-by: Ajeet Kumar Yadav 
> > ---
> >  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
> >
>