Re: [PATCH v6 1/8] iommu: provide early initialisation hook for IOMMU drivers

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Tuesday 02 December 2014 10:23:00 Marek Szyprowski wrote:
> >> +static inline void of_iommu_set_ops(struct device_node *np,
> >> +                                   const struct iommu_ops *ops)
> >> +{
> >> +       np->data = (struct iommu_ops *)ops;
> >> +}
> >> +
> >> +static inline struct iommu_ops *of_iommu_get_ops(struct device_node *np)
> >> +{
> >> +       return np->data;
> >> +}
> > This may collide with other users. While use of it is rare, PPC uses
> > it in its PCI code. The OF_DYNAMIC code frees it but never actually
> > sets it. There may be some coming usage with the DT overlay code or
> > that's just a bug. Pantelis or Grant can comment. If not, I think we
> > really should try to get rid of this pointer rather than expand it's
> > usage.
> 
> I think that for the initial version it is ok to use np->data. When 
> per-iommu
> controller structure is introduced later, it can be reused also for 
> performing
> of_node to iommu_ops lookup, because IOMMU framework will need to keep track
> on all such iommu controllers anyway.

Agreed. I think in the long run, we will have a 'struct iommu' that is
added into a global linked list and that contains (among other things)
an iommu_ops pointer and a device_node pointer. The of_iommu_get_ops
function then walks the list to find the right iommu instance.

	Arnd