linux-kernel - Re: [PATCH 08/10] swiotlb-xen: introduce phys_to_dma/dma_to

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Date:   Fri, 22 May 2020 10:34:13 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>, jgross@...e.com,
        konrad.wilk@...cle.com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano.stabellini@...inx.com>
Subject: Re: [PATCH 08/10] swiotlb-xen: introduce phys_to_dma/dma_to_phys
 translations

On Thu, 21 May 2020, Boris Ostrovsky wrote:
> On 5/20/20 7:45 PM, Stefano Stabellini wrote:
> > From: Stefano Stabellini <stefano.stabellini@...inx.com>
> >
> > Call dma_to_phys in is_xen_swiotlb_buffer.
> > Call phys_to_dma in xen_phys_to_bus.
> > Call dma_to_phys in xen_bus_to_phys.
> >
> > Everything is taken care of by these changes except for
> > xen_swiotlb_alloc_coherent and xen_swiotlb_free_coherent, which need a
> > few explicit phys_to_dma/dma_to_phys calls.
> >
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@...inx.com>
> > ---
> >  drivers/xen/swiotlb-xen.c | 20 ++++++++++++--------
> >  1 file changed, 12 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> > index c50448fd9b75..d011c4c7aa72 100644
> > --- a/drivers/xen/swiotlb-xen.c
> > +++ b/drivers/xen/swiotlb-xen.c
> > @@ -64,14 +64,16 @@ static inline dma_addr_t xen_phys_to_bus(struct device *dev, phys_addr_t paddr)
> >  
> >  	dma |= paddr & ~XEN_PAGE_MASK;
> >  
> > -	return dma;
> > +	return phys_to_dma(dev, dma);
> >  }
> >  
> > -static inline phys_addr_t xen_bus_to_phys(struct device *dev, dma_addr_t baddr)
> > +static inline phys_addr_t xen_bus_to_phys(struct device *dev,
> > +					  dma_addr_t dma_addr)
> 
> 
> Since now dma address != bus address this is no longer
> xen_bus_to_phys(). (And I guess the same is rue for xen_phys_to_bus()).

Should I rename them to xen_dma_to_phys and xen_phys_to_dma?

 
> >  {
> > +	phys_addr_t baddr = dma_to_phys(dev, dma_addr);
> >  	unsigned long xen_pfn = bfn_to_pfn(XEN_PFN_DOWN(baddr));
> > -	dma_addr_t dma = (dma_addr_t)xen_pfn << XEN_PAGE_SHIFT;
> > -	phys_addr_t paddr = dma;
> > +	phys_addr_t paddr = (xen_pfn << XEN_PAGE_SHIFT) |
> > +			    (baddr & ~XEN_PAGE_MASK);
> >  
> >  	paddr |= baddr & ~XEN_PAGE_MASK;
> 
> 
> This line needs to go, no?

Yes, good point