Re: [Xen-devel] [PATCH v9 01/18] arm: make SWIOTLB available

[Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>]

On Tue, Oct 29, 2013 at 10:20:23AM -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Oct 29, 2013 at 04:41:40AM +0000, Stefano Stabellini wrote:
> > ping?
> 
> You know you are pinging yourself, right ? :-)

And the patch was only Cc'd.  I'm starting to read stuff which isn't
flagged as having me in the To: line with less priority in recent times.

> > On Fri, 25 Oct 2013, Stefano Stabellini wrote:
> > > Russell,
> > > this is the only patch that needs an ack at the moment.
> > > As you commented on it before and I have already addressed your comments
> > > few versions ago, unless you have any complaints I am going to add it to
> > > linux-next and I am thinking of merging it during the next merge window.
> > > 
> > > On Fri, 25 Oct 2013, Stefano Stabellini wrote:
> > > > IOMMU_HELPER is needed because SWIOTLB calls iommu_is_span_boundary,
> > > > provided by lib/iommu_helper.c.
> > > > 
> > > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > > > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > > CC: will.deacon@xxxxxxx
> > > > CC: linux@xxxxxxxxxxxxxxxx
> > > > 
> > > > 
> > > > Changes in v8:
> > > > - use __phys_to_pfn and __pfn_to_phys.
> > > > 
> > > > Changes in v7:
> > > > - dma_mark_clean: empty implementation;
> > > > - in dma_capable use coherent_dma_mask if dma_mask hasn't been
> > > >   allocated.
> > > > 
> > > > Changes in v6:
> > > > - check for dev->dma_mask being NULL in dma_capable.
> > > > 
> > > > Changes in v5:
> > > > - implement dma_mark_clean using dmac_flush_range.
> > > > 
> > > > Changes in v3:
> > > > - dma_capable: do not treat dma_mask as a limit;
> > > > - remove SWIOTLB dependency on NEED_SG_DMA_LENGTH.
> > > > ---
> > > >  arch/arm/Kconfig                   |    6 +++++
> > > >  arch/arm/include/asm/dma-mapping.h |   37 
> > > > ++++++++++++++++++++++++++++++++++++
> > > >  2 files changed, 43 insertions(+), 0 deletions(-)
> > > > 
> > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > > index 1ad6fb6..b08374f 100644
> > > > --- a/arch/arm/Kconfig
> > > > +++ b/arch/arm/Kconfig
> > > > @@ -1872,6 +1872,12 @@ config CC_STACKPROTECTOR
> > > >           neutralized via a kernel panic.
> > > >           This feature requires gcc version 4.2 or above.
> > > >  
> > > > +config SWIOTLB
> > > > +       def_bool y
> > > > +
> > > > +config IOMMU_HELPER
> > > > +       def_bool SWIOTLB
> > > > +
> > > >  config XEN_DOM0
> > > >         def_bool y
> > > >         depends on XEN
> > > > diff --git a/arch/arm/include/asm/dma-mapping.h 
> > > > b/arch/arm/include/asm/dma-mapping.h
> > > > index 5b579b9..01b5a3d 100644
> > > > --- a/arch/arm/include/asm/dma-mapping.h
> > > > +++ b/arch/arm/include/asm/dma-mapping.h
> > > > @@ -10,6 +10,7 @@
> > > >  
> > > >  #include <asm-generic/dma-coherent.h>
> > > >  #include <asm/memory.h>
> > > > +#include <asm/cacheflush.h>

Why does this need to be here?  Your'e not adding anything which
needs it.

> > > > +static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t 
> > > > paddr)
> > > > +{
> > > > +       unsigned int offset = paddr & ~PAGE_MASK;
> > > > +       return pfn_to_dma(dev, __phys_to_pfn(paddr)) + offset;
> > > > +}
> > > > +
> > > > +static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t 
> > > > dev_addr)
> > > > +{
> > > > +       unsigned int offset = dev_addr & ~PAGE_MASK;
> > > > +       return __pfn_to_phys(dma_to_pfn(dev, dev_addr)) + offset;
> > > > +}

These look fine.

> > > > +static inline bool dma_capable(struct device *dev, dma_addr_t addr, 
> > > > size_t size)
> > > > +{
> > > > +       u64 limit, mask;
> > > > +       
> > > > +       if (dev->dma_mask)
> > > > +               mask = *dev->dma_mask;
> > > > +       else 
> > > > +               mask = dev->coherent_dma_mask;

This looks like a hack.  Either we want to use the streaming mask or
the coherent mask as appropriate for the caller.  That should be a choice
the caller makes, not the implementation of this behind the callers back.

> > > > +
> > > > +       if (mask == 0)
> > > > +               return 0;
> > > > +
> > > > +       limit = (mask + 1) & ~mask;
> > > > +       if (limit && size > limit)
> > > > +               return 0;
> > > > +
> > > > +       if ((addr | (addr + size - 1)) & ~mask)
> > > > +               return 0;
> > > > +
> > > > +       return 1;
> > > > +}

The remainder looks fine to me.

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