Re: [PATCH 2/2] iommu/arm-smmu: add support for iova_to_phys through ATS1PR

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

On Wed, Sep 24, 2014 at 09:34:26PM +0100, Mitchel Humpherys wrote:
> On Wed, Sep 24 2014 at 09:37:12 AM, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> wrote:
> > On Wed, Sep 24, 2014 at 02:12:00AM +0100, Mitchel Humpherys wrote:
> >> On Mon, Sep 22 2014 at 08:26:14 AM, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> wrote:
> >> > On Thu, Sep 11, 2014 at 07:30:44PM +0100, Mitchel Humpherys wrote:
> >> >> +		return arm_smmu_iova_to_phys_soft(domain, iova);
> >> >> +	}
> >> >> +
> >> >> +	phys = readl_relaxed(cb_base + ARM_SMMU_CB_PAR_LO);
> >> >> +	phys |= ((u64) readl_relaxed(cb_base + ARM_SMMU_CB_PAR_HI)) << 32;
> >> >> +
> >> >> +	if (phys & CB_PAR_F) {
> >> >> +		dev_err(dev, "translation fault on %s!\n", dev_name(dev));
> >> >> +		dev_err(dev, "PAR = 0x%llx\n", phys);
> >> >> +	}
> >> >> +	phys = (phys & 0xFFFFFFF000ULL) | (iova & 0x00000FFF);
> >> >
> >> > How does this work for 64k pages?
> >> 
> >> So at the moment we're always assuming that we're using v7/v8 long
> >> descriptor format, right?  All I see in the spec (14.5.15 SMMU_CBn_PAR)
> >> is that bits[47:12]=>PA[47:12]...  Or am I missing something completely?
> >
> > I think you've got 64k pages confused with the short-descriptor format.
> >
> > When we use 64k pages with long descriptors, you're masked off bits 15-12 of
> > the iova above, so you'll have a hole in the physical address afaict.
> 
> Even with long descriptors the spec says bits 15-12 should come from
> CB_PAR...  It makes no mention of reinterpreting those bits depending on
> the programmed page granule.  The only thing I can conclude from the
> spec is that hardware should be smart enough to do the right thing with
> bits 15-12 when the page granule is 64k.  Although even if hardware is
> smart enough I guess CB_PAR[15:12] should be the same as iova[15:12] for
> the 64k case?

Yeah, fair enough, the code you have should work correctly then.
Unfortunately, I don't have any suitable hardware on which to test it.

Will