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Re: [RFC PATCH-for-8.0 3/3] hw/net/xilinx_ethlite: Replace tswap32() by
From: |
Edgar E. Iglesias |
Subject: |
Re: [RFC PATCH-for-8.0 3/3] hw/net/xilinx_ethlite: Replace tswap32() by be32_to_cpu() |
Date: |
Tue, 13 Dec 2022 14:54:55 +0100 |
On Tue, Dec 13, 2022 at 01:53:15PM +0000, Peter Maydell wrote:
> On Tue, 13 Dec 2022 at 12:52, Philippe Mathieu-Daudé <philmd@linaro.org>
> wrote:
> >
> > This partly revert commit d48751ed4f ("xilinx-ethlite:
> > Simplify byteswapping to/from brams") which states the
> > packet data is stored in big-endian.
> >
> > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>
> > @@ -102,8 +102,8 @@ eth_read(void *opaque, hwaddr addr, unsigned int size)
> > D(qemu_log("%s " TARGET_FMT_plx "=%x\n", __func__, addr * 4,
> > r));
> > break;
> >
> > - default:
> > - r = tswap32(s->regs[addr]);
> > + default: /* Packet data */
> > + r = be32_to_cpu(s->regs[addr]);
> > break;
> > }
> > return r;
> > @@ -160,8 +160,8 @@ eth_write(void *opaque, hwaddr addr,
> > s->regs[addr] = value;
> > break;
> >
> > - default:
> > - s->regs[addr] = tswap32(value);
> > + default: /* Packet data */
> > + s->regs[addr] = cpu_to_be32(value);
> > break;
> > }
> > }
>
> This is a change of behaviour for this device in the
> qemu-system-microblazeel petalogix-s3adsp1800 board, because
> previously on that system the bytes of the rx buffer would
> appear in the registers in little-endian order and now they
> will appear in big-endian order.
>
> Edgar, do you know what the real hardware does here ?
>
Yeah, I think these tx/rx buffers (the default case with tswap32) should be
modelled as plain RAM's (they are just RAM's on real HW).
Because we're modeling as MMIO regs, I think we get into endianness trouble
when the ethernet
output logic treats the content as a blob (thus the need for byteswaps). Does
that make sense?
Cheers,
Edgar
- Re: [RFC PATCH-for-8.0 1/3] hw/ppc: Replace tswap32() by const_le32(), (continued)
[RFC PATCH-for-8.0 3/3] hw/net/xilinx_ethlite: Replace tswap32() by be32_to_cpu(), Philippe Mathieu-Daudé, 2022/12/13
Re: [RFC PATCH-for-8.0 0/3] hw/ppc: Remove tswap() calls, Cédric Le Goater, 2022/12/13