From: will.deacon@arm.com (Will Deacon)
Date: Tue, 21 Mar 2017 18:17:29 +0000
Subject: [PATCH v2 5/5] iommu: Allow default domain type to be set on the
 kernel command line
In-Reply-To: <807ecbb0-c9d7-fc0a-25d2-93b5c4374107@arm.com>
References: <1489178976-15353-1-git-send-email-will.deacon@arm.com>
 <1489178976-15353-6-git-send-email-will.deacon@arm.com>
 <20170321154527.GB29659@8bytes.org>
 <20170321172137.GF30948@arm.com>
 <807ecbb0-c9d7-fc0a-25d2-93b5c4374107@arm.com>
Message-ID: <20170321181729.GG30948@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, Mar 21, 2017 at 05:46:29PM +0000, Robin Murphy wrote:
> On 21/03/17 17:21, Will Deacon wrote:
> > On Tue, Mar 21, 2017 at 04:45:27PM +0100, Joerg Roedel wrote:
> >> On Fri, Mar 10, 2017 at 08:49:36PM +0000, Will Deacon wrote:
> >>> @@ -1014,8 +1027,8 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
> >>>  	 * IOMMU driver.
> >>>  	 */
> >>>  	if (!group->default_domain) {
> >>> -		group->default_domain = __iommu_domain_alloc(dev->bus,
> >>> -							     IOMMU_DOMAIN_DMA);
> >>> +		group->default_domain =
> >>> +			__iommu_domain_alloc(dev->bus, iommu_def_domain_type);
> >>
> >> It would be good to have a fall-back here if we are talking to an IOMMU
> >> driver that uses default domains, but does not support identity-mapped
> >> domains (yet). Exynos and Rockchip IOMMU drivers seem to fall into this
> >> category. A dev_warn() also makes sense in case allocating a identity
> >> domain fails.
> > 
> > Sure, something like the diff below?
> > 
> > Will
> > 
> > --->8
> > 
> > 
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 42a842e3f95f..f787626a745d 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -1027,10 +1027,19 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
> >  	 * IOMMU driver.
> >  	 */
> >  	if (!group->default_domain) {
> > -		group->default_domain =
> > -			__iommu_domain_alloc(dev->bus, iommu_def_domain_type);
> > +		struct iommu_domain *dom;
> > +
> > +		dom = __iommu_domain_alloc(dev->bus, iommu_def_domain_type);
> > +		if (!dom) {
> > +			dev_warn(dev,
> > +				 "failed to allocate default IOMMU domain of type %u; falling back to IOMMU_DOMAIN_DMA",
> > +				 iommu_def_domain_type);
> 
> Conversely, that's going to be noisy if iommu_def_domain_type was
> IOMMU_DOMAIN_DMA to begin with. I think it makes sense to warn if the
> user asked for a specific default domain type on the command line and
> that didn't work, but maybe not to bother otherwise. Plus, if they asked
> for passthrough, then not allocating a default domain at all is probably
> closer to the desired result than installing a DMA ops domain would be.

You're right -- I'll hack this about to check if the default type isn't
DOMAIN_DMA before warning about the allocation failure.

Cheers,

Will