Re: [Qemu-devel] [PATCH] xhci: Fix some DMA host endian bugs

[David Gibson]

On Fri, Nov 02, 2012 at 08:31:23AM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> > +static inline void xhci_dma_write_u32s(XHCIState *xhci, dma_addr_t addr,
> > +                                       uint32_t *buf, size_t len)
> > +{
> > +    int i;
> > +
> > +    for (i = 0; i < (len / sizeof(uint32_t)); i++) {
> > +        buf[i] = cpu_to_le32(buf[i]);
> > +    }
> > +    pci_dma_write(&xhci->pci_dev, addr, buf, len);
> > +}
> 
> I think we should use a temporary buffer here, otherwise you leave the
> values byteswapped in buf which likely has unwanted side effects.

Yeah, I wondered about that.  I did check that the side-effect doesn't
matter in any of the existing callers, so I left it that way to avoid
the extra copies.  But you're right, it's a pretty subtle constraint
that could easily be broken by future changes.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson