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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f227325bcsm980168f8f.50.2025.02.12.10.17.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Feb 2025 10:17:35 -0800 (PST) Message-ID: <672045c1-9b09-4b7b-9bed-fa990129ce2c@linaro.org> Date: Wed, 12 Feb 2025 19:17:35 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 01/11] hw/qdev-properties-system: Introduce EndianMode QAPI enum To: BALATON Zoltan Cc: Thomas Huth , qemu-devel@nongnu.org, qemu-riscv@nongnu.org, qemu-ppc@nongnu.org, "Edgar E. Iglesias" , Alistair Francis , Richard Henderson , Markus Armbruster , qemu-arm@nongnu.org, =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= References: <20250212112413.37553-1-philmd@linaro.org> <20250212112413.37553-2-philmd@linaro.org> <50ba4e4b-4124-46bb-bb84-4758ce9c5e66@linaro.org> <3b3baed4-0d79-3a28-40cd-e1835e078863@eik.bme.hu> <6e707c7f-b94c-47ef-83ab-795605e27963@linaro.org> Content-Language: en-US From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::333; envelope-from=philmd@linaro.org; helo=mail-wm1-x333.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 12/2/25 17:23, BALATON Zoltan wrote: > On Wed, 12 Feb 2025, Philippe Mathieu-Daudé wrote: >> On 12/2/25 14:53, Philippe Mathieu-Daudé wrote: >>> On 12/2/25 13:56, BALATON Zoltan wrote: >>>> On Wed, 12 Feb 2025, Philippe Mathieu-Daudé wrote: >>>>> On 12/2/25 12:37, Thomas Huth wrote: >>>>>> On 12/02/2025 12.24, Philippe Mathieu-Daudé wrote: >>>>>>> Introduce the EndianMode type and the DEFINE_PROP_ENDIAN() macros. >>>>>>> Endianness can be BIG, LITTLE or unspecified (default). >>>>>>> >>>>>>> Signed-off-by: Philippe Mathieu-Daudé >>>>>>> --- >>>>>>>   qapi/common.json                    | 16 ++++++++++++++++ >>>>>>>   include/hw/qdev-properties-system.h |  7 +++++++ >>>>>>>   hw/core/qdev-properties-system.c    | 11 +++++++++++ >>>>>>>   3 files changed, 34 insertions(+) >>>>>>> +{ 'enum': 'EndianMode', >>>>>>> +  'data': [ 'little', 'big', 'unspecified' ] } >>>>>> >>>>>> Should 'unspecified' come first? ... so that it gets the value 0, >>>>>> i.e. when someone forgets to properly initialize a related >>>>>> variable, the chances are higher that it ends up as "unspecified" >>>>>> than as "little" ? >>>>> >>>>> Hmm but then in this series the dual-endianness regions are defined >>>>> as: >>>>> >>>>> +static const MemoryRegionOps pic_ops[2] = { >>>>> +    [0 ... 1] = { >>>> >>>> This is already confusing as you'd have to know that 0 and 1 here >>>> means ENDIAN_MODE_LITTLE and ENDIAN_MODE_BIG (using those constants >>>> here as well might be clearer). It's easy to miss what this does so >> >> At this point 0 / 1 only mean "from the index #0 included to the index >> #1 included", 0 being the first one and 1 the last one. >> >>>> maybe repeating the definitions for each case would be longer but >>>> less confusing and then it does not matter what the values are. >> >> This is what I tried to do with: >> >> +    [ENDIAN_MODE_BIG].endianness = DEVICE_BIG_ENDIAN, >> +    [ENDIAN_MODE_LITTLE].endianness = DEVICE_LITTLE_ENDIAN, >> }; >> >> but in v7 we are back of picking an arbitrary value. >> >>>> Or what uses the ops.endianness now should look at the property >>>> introduced by this patch to avoid having to propagate it like below >>>> and drop the ops.endianness? Or it should move to the memory region >>>> and set when the ops are assigned? >>> >>> I'm not understanding well what you ask, but maybe the answer is in >>> v7 :) > > I'm not sure I understand it well either. I think what I was asking > about is the same as what Thomas asked if this could be avoided to make > it necessary to allocate two separate ops for this. Looks like from now > on this ops struct should really loose the endianness value and this > should be assigned when the ops is added to the io region because that's > where it decides which endianness is it based on the property added in > this series. But I don't know if that could be done or would need deeper > changes as what later uses this ops struct might not have access to the > property and if we have a single ops struct it may need to be copied to > set different endianness intstead of just referencing it. So I'm not > sure there's a better way but I think this change makes an already > cryptic boiler plate even more confusing for people less knowledgeable > about QEMU and C programming so it makes even harder to write devices. > But as long as it's just a few devices that need to work with different > endianness then it might be OK. But wasn't that what NATIVE_ENDIAN was > meant for? What can't that be kept then? Moving toward a single binary able to run heterogeneous machines, we can't rely on a particular target endianness, so we need to remove DEVICE_NATIVE_ENDIAN. The endianness is a property a device / machine, not of the binary.