Re: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2018-10-03 at 16:10 -0700, Alexander Duyck wrote:
> > -        * Because 32-bit DMA masks are so common we expect every architecture
> > -        * to be able to satisfy them - either by not supporting more physical
> > -        * memory, or by providing a ZONE_DMA32.  If neither is the case, the
> > -        * architecture needs to use an IOMMU instead of the direct mapping.
> > -        */
> > -       if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
> > +       u64 min_mask;
> > +
> > +       if (IS_ENABLED(CONFIG_ZONE_DMA))
> > +               min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
> > +       else
> > +               min_mask = DMA_BIT_MASK(32);
> > +
> > +       min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
> > +
> > +       if (mask >= phys_to_dma(dev, min_mask))
> >                  return 0;
> > -#endif
> >          return 1;
> >   }
> 
> So I believe I have run into the same issue that Guenter reported. On
> an x86_64 system w/ Intel IOMMU. I wasn't able to complete boot and
> all probe attempts for various devices were failing with -EIO errors.
> 
> I believe the last mask check should be "if (mask < phys_to_dma(dev,
> min_mask))" not a ">=" check.

Right, that test is backwards. I needed to change it here too (powermac
with the rest of the powerpc series).

Cheers,
Ben.