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

From: Will Deacon <will@kernel.org>
To: Yong Wu <yong.wu@mediatek.com>
Cc: youlin.pei@mediatek.com, devicetree@vger.kernel.org,
	Nicolas Boichat <drinkcat@chromium.org>,
	srv_heupstream@mediatek.com, chao.hao@mediatek.com,
	Joerg Roedel <joro@8bytes.org>,
	linux-kernel@vger.kernel.org, Evan Green <evgreen@chromium.org>,
	Tomasz Figa <tfiga@google.com>,
	iommu@lists.linux-foundation.org,
	Rob Herring <robh+dt@kernel.org>,
	linux-mediatek@lists.infradead.org,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	anan.sun@mediatek.com, Robin Murphy <robin.murphy@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 07/33] iommu: Avoid reallocate default domain for a group
Date: Thu, 28 Jan 2021 21:14:42 +0000	[thread overview]
Message-ID: <20210128211442.GB3531@willie-the-truck> (raw)
In-Reply-To: <20210128211020.GA3531@willie-the-truck>

On Thu, Jan 28, 2021 at 09:10:20PM +0000, Will Deacon wrote:
> 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@mediatek.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.

Argh, except that this version of the patches doesn't apply :)

So after all that, please go ahead and post a v7 ASAP based on this branch:

https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=for-joerg/mtk

Will

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