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
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