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

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Message-ID: <20210128211020.GA3531@willie-the-truck>
Date:   Thu, 28 Jan 2021 21:10:20 +0000
From:   Will Deacon <will@...nel.org>
To:     Yong Wu <yong.wu@...iatek.com>
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 Wed, Jan 27, 2021 at 05:39:16PM +0800, Yong Wu wrote:
> 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.

Actually, looking at this again, if we're dropping this patch and patch 6
just needs the kfree() moving about, then there's no need to repost. The
issue that Robin and Paul are discussing can be handled separately.

Will