linux-kernel - Re: [PATCH v6 07/33] iommu: Avoid reallocate default domain for a group

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Date:   Wed, 27 Jan 2021 17:39:16 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Will Deacon <will@...nel.org>
CC:     Joerg Roedel <joro@...tes.org>, Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Evan Green <evgreen@...omium.org>,
        Tomasz Figa <tfiga@...gle.com>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <youlin.pei@...iatek.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        <anan.sun@...iatek.com>, <chao.hao@...iatek.com>
Subject: Re: [PATCH v6 07/33] iommu: Avoid reallocate default domain for a
 group

On Tue, 2021-01-26 at 22:23 +0000, Will Deacon wrote:
> On Mon, Jan 11, 2021 at 07:18:48PM +0800, Yong Wu wrote:
> > If group->default_domain exists, avoid reallocate it.
> > 
> > In some iommu drivers, there may be several devices share a group. Avoid
> > realloc the default domain for this case.
> > 
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > ---
> >  drivers/iommu/iommu.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 3d099a31ddca..f4b87e6abe80 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -266,7 +266,8 @@ int iommu_probe_device(struct device *dev)
> >  	 * support default domains, so the return value is not yet
> >  	 * checked.
> >  	 */
> > -	iommu_alloc_default_domain(group, dev);
> > +	if (!group->default_domain)
> > +		iommu_alloc_default_domain(group, dev);
> 
> I don't really get what this achieves, since iommu_alloc_default_domain()
> looks like this:
> 
> static int iommu_alloc_default_domain(struct iommu_group *group,
> 				      struct device *dev)
> {
> 	unsigned int type;
> 
> 	if (group->default_domain)
> 		return 0;
> 
> 	...
> 
> in which case, it should be fine?

oh. sorry, I overlooked this. the current code is enough.
I will remove this patch. and send the next version in this week.
Thanks very much.

> 
> Will