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

    Will

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