Re: [RFC PATCH v3 3/7] iommu: add new iommu_ops callback for adding an OF device

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

On Mon, Sep 15, 2014 at 12:57:38PM +0100, Marek Szyprowski wrote:
> Hello,

Hi Marek,

Thanks for looking again at this -- I'll take at look at your exynos series
when I'm back in the UK next week.

> On 2014-09-12 18:34, Will Deacon wrote:
> > This patch adds a new function to the iommu_ops structure to allow an
> > OF device to be added to a specific IOMMU instance using the recently
> > merged generic devicetree binding for IOMMUs. The callback (of_xlate)
> > takes a struct device representing the master and an of_phandle_args
> > representing the IOMMU and the correspondong IDs for the new master.
> >
> > Signed-off-by: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>
> > ---
> >   include/linux/iommu.h | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 4256f3ce1673..821eb0bd9f6c 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -21,6 +21,7 @@
> >   
> >   #include <linux/errno.h>
> >   #include <linux/err.h>
> > +#include <linux/of.h>
> >   #include <linux/types.h>
> >   #include <trace/events/iommu.h>
> >   
> > @@ -140,6 +141,10 @@ struct iommu_ops {
> >   	/* Get the numer of window per domain */
> >   	u32 (*domain_get_windows)(struct iommu_domain *domain);
> >   
> > +#ifdef CONFIG_OF_IOMMU
> > +	int (*of_xlate)(struct device *dev, struct of_phandle_args *args);
> > +#endif
> 
> 
> If I understand correctly, this callback is intended to do per-master 
> initialization
> of the iommu structures required by the given iommu driver (I stored them in
> dev->archdata.iommu). However I really don't get what is the meaning of 
> the return
> value. Is it a boolean value? It is used only by of_iommu_configure to 
> check if
> the parse loop should be terminated...

It should probably return 0 on success, < 0 otherwise. I'll fix
of_iommu_configure to check for < 0 and only exit the loop then. The idea is
that we don't swizzle the DMA ops for a device to IOMMU ops if of_xlate
failed for any of its IDs.

Will