Re: [PATCH 17/18] media/omap3isp: Clean up IOMMU workaround

[Robin Murphy]

On 2020-08-20 20:55, Sakari Ailus wrote:
> On Thu, Aug 20, 2020 at 06:25:19PM +0100, Robin Murphy wrote:
> > On 2020-08-20 17:53, Sakari Ailus wrote:
> > > Hi Robin,
> > >
> > > On Thu, Aug 20, 2020 at 04:08:36PM +0100, Robin Murphy wrote:
> > > > Now that arch/arm is wired up for default domains and iommu-dma, devices
> > > > behind IOMMUs will get mappings set up automatically as appropriate, so
> > > > there is no need for drivers to do so manually.
> > > >
> > > > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> > >
> > > Thanks for the patch.
> >
> > Many thanks for testing so quickly!
> >
> > > I haven't looked at the details but it seems that this causes the buffer
> > > memory allocation to be physically contiguous, which causes a failure to
> > > allocate video buffers of entirely normal size. I guess that was not
> > > intentional?
> >
> > Hmm, it looks like the device ends up with the wrong DMA ops, which implies
> > something didn't go as expected with the earlier IOMMU setup and default
> > domain creation. Chances are that either I missed some subtlety in the
> > omap_iommu change, or I've fundamentally misjudged how the ISP probing works
> > and it never actually goes down the of_iommu_configure() path in the first
> > place. Do you get any messages from the IOMMU layer earlier on during boot?
>
> I do get these:
>
> [    2.934936] iommu: Default domain type: Translated
> [    2.940917] omap-iommu 480bd400.mmu: 480bd400.mmu registered
> [    2.946899] platform 480bc000.isp: Adding to iommu group 0

So that much looks OK, if there are no obvious errors. Unfortunately 
there's no easy way to tell exactly what of_iommu_configure() is doing 
(beyond enabling a couple of vague debug messages). The first thing I'll 
do tomorrow is double-check whether it's really working on my boards 
here, or whether I was just getting lucky with CMA... (I assume you 
don't have CMA enabled if you're ending up in remap_allocator_alloc())

Robin.