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[81.232.4.135]) by smtp.gmail.com with ESMTPSA id s13-20020a2eb8cd000000b00279f302f652sm278625ljp.111.2022.12.13.06.23.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Dec 2022 06:23:42 -0800 (PST) Date: Tue, 13 Dec 2022 15:23:41 +0100 From: "Edgar E. Iglesias" To: Peter Maydell Cc: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , qemu-devel@nongnu.org, Daniel Henrique Barboza , BALATON Zoltan , Alex =?iso-8859-1?Q?Benn=E9e?= , Alistair Francis , David Gibson , Jason Wang , =?iso-8859-1?Q?C=E9dric?= Le Goater , Greg Kurz , qemu-arm@nongnu.org, qemu-ppc@nongnu.org Subject: Re: [RFC PATCH-for-8.0 3/3] hw/net/xilinx_ethlite: Replace tswap32() by be32_to_cpu() Message-ID: References: <20221213125218.39868-1-philmd@linaro.org> <20221213125218.39868-4-philmd@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-TUID: StbntMSFbjiR On Tue, Dec 13, 2022 at 02:18:42PM +0000, Peter Maydell wrote: > On Tue, 13 Dec 2022 at 14:14, Edgar E. Iglesias > wrote: > > > > On Tue, Dec 13, 2022 at 01:53:15PM +0000, Peter Maydell wrote: > > > On Tue, 13 Dec 2022 at 12:52, Philippe Mathieu-Daudé 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 > > > > > > > @@ -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? > > As a concrete question: if I do a 32-bit load from the buffer > register into a CPU register, do I get a different value > on the BE microblaze hardware vs LE microblaze ? Yes, I beleive so. If the CPU stores the value and reads it back, you get the same. But the representation on the RAM's is different between LE/BE. But if the Ethernet logic writes Ethernet packet data into the buffer, LE and BE MicroBlazes will read differient values from the buffers. These buffer "registers" are just RAM's I beleive. Best regards, Edgar