Re: [PATCH v3 5/6] iommu/mediatek: Add mt8173 IOMMU driver

[Robin Murphy]

On 27/07/15 16:31, Russell King - ARM Linux wrote:
> On Mon, Jul 27, 2015 at 02:23:26PM +0100, Robin Murphy wrote:
> > On 16/07/15 10:04, Yong Wu wrote:
> > > This patch adds support for mediatek m4u (MultiMedia Memory Management
> > > Unit).
> > >
> > > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> > [...]
> > > +static void mtk_iommu_flush_pgtable(void *ptr, size_t size, void *cookie)
> > > +{
> > > +       struct mtk_iommu_domain *domain = cookie;
> > > +       unsigned long offset = (unsigned long)ptr & ~PAGE_MASK;
> > > +
> > > +       dma_map_page(domain->data->dev, virt_to_page(ptr), offset,
> > > +                    size, DMA_TO_DEVICE);
> >
> > Nit: this looks like it may as well be dma_map_single.
> >
> > It would probably be worth following it with a matching unmap too, just to
> > avoid any possible leakage bugs (especially if this M4U ever appears in a
> > SoC supporting RAM above the 32-bit boundary).
>
> Why not do the job properly?  Take a look at how I implemented the
> streaming DMA API on Tegra SMMU (patch set recently sent out earlier
> today).
>
> There's no need for hacks like dma_map_page() (and discarding it's
> return value) or dma_map_page() followed by dma_unmap_page().

Indeed, as it happens I do have a branch where I prototyped that for the 
long-descriptor io-pgtable-arm code a while ago; this discussion has 
prompted me to dig it up again. Stay tuned, folks...

Robin.

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