Re: [PATCH v2 13/13] iommu/rockchip: Support sharing IOMMU between masters

[JeffyChen]

Hi Robin,

On 01/17/2018 09:00 PM, Robin Murphy wrote:
> On 16/01/18 13:25, Jeffy Chen wrote:
> > There would be some masters sharing the same IOMMU device. Put them in
> > the same iommu group and share the same iommu domain.
> >
> > Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
> > ---
> >
> > Changes in v2: None
> >
> >   drivers/iommu/rockchip-iommu.c | 39
> > +++++++++++++++++++++++++++++++--------
> >   1 file changed, 31 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/iommu/rockchip-iommu.c
> > b/drivers/iommu/rockchip-iommu.c
> > index c8de1456a016..6c316dd0dd2d 100644
> > --- a/drivers/iommu/rockchip-iommu.c
> > +++ b/drivers/iommu/rockchip-iommu.c
> > @@ -100,11 +100,13 @@ struct rk_iommu {
> >       struct iommu_device iommu;
> >       struct list_head node; /* entry in rk_iommu_domain.iommus */
> >       struct iommu_domain *domain; /* domain to which iommu is
> > attached */
> > +    struct iommu_group *group;
> >       struct mutex pm_mutex; /* serializes power transitions */
> >   };
> >   struct rk_iommudata {
> >       struct device_link *link; /* runtime PM link from IOMMU to
> > master */
> > +    struct iommu_domain *domain; /* domain to which device is
> > attached */
>
> I don't see why this is needed - for example, mtk_iommu does the same
> thing without needing to track the active domain in more than one place.
>
> Fundamentally, for this kind of IOMMU without the notion of multiple
> translation contexts, the logic should look like:
>
>      iommudrv_attach_device(dev, domain) {
>          iommu = dev_get_iommu(dev);
>          if (iommu->curr_domain != domain) {
>              update_hw_state(iommu, domain);
>              iommu->curr_domain = domain;
>          }
>      }
>
> which I think is essentially what you have anyway. When a group contains
> multiple devices, you update the IOMMU state for the first device, then
> calls for subsequent devices in the group do nothing since they see the
> IOMMU state is already up-to-date with the new domain.
right, will remove it.
> Robin.