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Re: [Qemu-devel] [PATCH 01/15] exec: introduce endianness swapped mmio
From: |
Paul Brook |
Subject: |
Re: [Qemu-devel] [PATCH 01/15] exec: introduce endianness swapped mmio |
Date: |
Fri, 26 Nov 2010 23:47:45 +0000 |
User-agent: |
KMail/1.13.5 (Linux/2.6.36-trunk-amd64; KDE/4.4.5; x86_64; ; ) |
> > diff --git a/exec.c b/exec.c
> > index db9ff55..f54a360 100644
> > --- a/exec.c
> > +++ b/exec.c
> >
> > @@ -3370,6 +3474,22 @@ static int cpu_register_io_memory_fixed(int
> > io_index,
> >
> > }
> > io_mem_opaque[io_index] = opaque;
> >
> > + switch (endian) {
> > + case DEVICE_BIG_ENDIAN:
> > +#ifndef TARGET_WORDS_BIGENDIAN
> > + swapendian_init(io_index);
> > +#endif
> > + break;
>
> So basically, you just moved the #ifdefs to another place. :)
Many #ifdefs inconsistently scattered through all the device code have been
replaced by a single #ifdef.
> Shouldn't this be dependent on the CPU state and determined at
> runtime? Thinking of MSR LE bit on ppc. I guess QEMU doesn't support
> bi-endian ppc today, as does the 970, but it would be nice to keep it
> in mind.
Switching endianness of a CPU generally does not effect the endianness of the
CPU/peripheral busses. It makes the CPU byteswap accesses before they are
seen by either memory or devices.
In theory it might be possible to avoid redundant byteswaps if you're really
clever. In practice you still have to handle the fact that your devices are a
different endianness to RAM, so it probably doesn't gain you a whole lot.
Paul
- [Qemu-devel] [PATCH 00/15] [RFC] MMIO endianness cleanup, Alexander Graf, 2010/11/25
- [Qemu-devel] [PATCH 04/15] dbdma: Make little endian, Alexander Graf, 2010/11/25
- [Qemu-devel] [PATCH 03/15] Make simple io mem handler endian aware, Alexander Graf, 2010/11/25
- [Qemu-devel] [PATCH 06/15] uninorth: Get rid of bswap, Alexander Graf, 2010/11/25
- [Qemu-devel] [PATCH 07/15] e1000: Make little endian, Alexander Graf, 2010/11/25
- [Qemu-devel] [PATCH 12/15] rtl8139: Declare as little endian, Alexander Graf, 2010/11/25
- [Qemu-devel] [PATCH 01/15] exec: introduce endianness swapped mmio, Alexander Graf, 2010/11/25
- Re: [Qemu-devel] [PATCH 01/15] exec: introduce endianness swapped mmio, Gleb Natapov, 2010/11/28
[Qemu-devel] [PATCH 05/15] pci-host: Delegate bswap to mmio layer, Alexander Graf, 2010/11/25
[Qemu-devel] [PATCH 13/15] heathrow_pic: Declare as little endian, Alexander Graf, 2010/11/25
[Qemu-devel] [PATCH 11/15] openpic: Replace explicit byte swap with endian hints, Alexander Graf, 2010/11/25
[Qemu-devel] [PATCH 15/15] usb_ohci: Always use little endian, Alexander Graf, 2010/11/25
[Qemu-devel] [PATCH 08/15] prep: Declare as little endian, Alexander Graf, 2010/11/25