[Qemu-devel] Re: [PATCH] Always swap endianness in DBDMA

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Dec 22, 2009 at 11:24:18AM +0100, Alexander Graf wrote:
> When we get an MMIO request, we always get variables in host endianness. The
> only time we need to actually reverse byte order is when we read bytes from
> guest memory.
> 
> Apparently the DBDMA implementation is different there. A lot of the logic
> in there depends on values being big endian. Now, qemu does all the conversion
> in the MMIO handlers for us already though, so it turns out that we're in
> the same byte order from a C point of view, but cpu_to_be32 and be32_to_cpu
> end up being nops.
> 
> This makes the code work differently on x86 (little endian) than on ppc (big
> endian). On x86 it works, on ppc it doesn't.
> 
> This patch (while being seriously hacky and ugly) makes dbdma emulation work
> on ppc hosts. I'll leave the real fixing to someone else.

Come on, 

#define cpu_to_dbdma32 bswap32
#define dbdma_to_cpu32 bswap32

and then

s/cpu_to_be32/cpu_to_dbdma32/g
s/be32_to_cpu/dbdma32_to_cpu/g

is not too hard, is it?

> Signed-off-by: Alexander Graf <agraf@suse.de>
> CC: Laurent Vivier <Laurent@vivier.eu>
> ---
>  hw/mac_dbdma.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/hw/mac_dbdma.c b/hw/mac_dbdma.c
> index 98dccfd..4dbfc16 100644
> --- a/hw/mac_dbdma.c
> +++ b/hw/mac_dbdma.c
> @@ -40,6 +40,14 @@
>  #include "isa.h"
>  #include "mac_dbdma.h"
>  
> +/*
> + * XXX This is just plain wrong. Apparently we don't want to have big endian
> + *     values, but reversed endian ones. The code as is doesn't work on big
> + *     endian hosts. With these defines it does.
> + */
> +#define cpu_to_be32 bswap32
> +#define be32_to_cpu bswap32
> +
>  /* debug DBDMA */
>  //#define DEBUG_DBDMA
>  
> -- 
> 1.6.0.2
> 
>