On Wed, Dec 23, 2009 at 10:29:53AM +0100, Alexander Graf wrote: > > On 23.12.2009, at 07:12, Aurelien Jarno wrote: > > > On Tue, Dec 22, 2009 at 02:45:17PM +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. > > > > I have to say I found it too hacky to be included in QEMU. I would > > prefer if someone can provide a real fix. > > Looking at hw/pci_host_template.h I'm actually more confident now that this > is actually the correct solution. We don't want big endian or little endian, > we want reversed endian variables. >
I guess it's the same problem, that is the bswap is there to emulate the fact that the bus is connected backward. Then I guess that the bswap should also depends on TARGET_WORDS_BIGENDIAN, even if this file is currently only compiled for big endian targets. Also a comment might be a good idea. Then I guess the patch is acceptable into QEMU. -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurel...@aurel32.net http://www.aurel32.net
