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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38dbdd36967sm2421995f8f.37.2025.02.06.10.43.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Feb 2025 10:43:11 -0800 (PST) Message-ID: Date: Thu, 6 Feb 2025 19:43:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 11/16] hw/microblaze: Support various endianness for s3adsp1800 machines To: =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= Cc: Michal Simek , qemu-devel@nongnu.org, qemu-arm@nongnu.org, Anton Johansson , Jason Wang , Paolo Bonzini , Alistair Francis , Thomas Huth , Richard Henderson , Peter Maydell , Markus Armbruster , =?UTF-8?Q?Alex_Benn=C3=A9e?= , "Edgar E. Iglesias" References: <20250206131052.30207-1-philmd@linaro.org> <20250206131052.30207-12-philmd@linaro.org> <4624f149-76d0-4da5-8f13-8c015043c335@linaro.org> <3156dc3b-9553-4b5f-a934-f29ee0601887@linaro.org> <63f1130e-a30d-4416-ae74-374f1fd94dbe@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::435; envelope-from=philmd@linaro.org; helo=mail-wr1-x435.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=ham 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 6/2/25 19:29, Daniel P. Berrangé wrote: > On Thu, Feb 06, 2025 at 07:24:55PM +0100, Philippe Mathieu-Daudé wrote: >> +Michal >> >> On 6/2/25 19:06, Daniel P. Berrangé wrote: >>> On Thu, Feb 06, 2025 at 06:49:38PM +0100, Philippe Mathieu-Daudé wrote: >>>> On 6/2/25 18:12, Daniel P. Berrangé wrote: >>>>> On Thu, Feb 06, 2025 at 04:04:20PM +0100, Philippe Mathieu-Daudé wrote: >>>>>> On 6/2/25 15:31, Daniel P. Berrangé wrote: >>>>>>> On Thu, Feb 06, 2025 at 02:53:58PM +0100, Philippe Mathieu-Daudé wrote: >>>>>>>> Hi Daniel, >>>>>>>> >>>>>>>> On 6/2/25 14:20, Daniel P. Berrangé wrote: >>>>>>>>> On Thu, Feb 06, 2025 at 02:10:47PM +0100, Philippe Mathieu-Daudé wrote: >>>>>>>>>> Introduce an abstract machine parent class which defines >>>>>>>>>> the 'little_endian' property. Duplicate the current machine, >>>>>>>>>> which endian is tied to the binary endianness, to one big >>>>>>>>>> endian and a little endian machine; updating the machine >>>>>>>>>> description. Keep the current default machine for each binary. >>>>>>>>>> >>>>>>>>>> 'petalogix-s3adsp1800' machine is aliased as: >>>>>>>>>> - 'petalogix-s3adsp1800-be' on big-endian binary, >>>>>>>>>> - 'petalogix-s3adsp1800-le' on little-endian one. >>>>>>>>> >>>>>>>>> Does it makes sense to expose these as different machine types ? >>>>>>>>> >>>>>>>>> If all the HW is identical in both cases, it feels like the >>>>>>>>> endianness could just be a bool property of the machine type, >>>>>>>>> rather than a new machine type. >>>>>>>> >>>>>>>> Our test suites expect "qemu-system-foo -M bar" to work out of >>>>>>>> the box, we can not have non-default properties. >>>>>>>> >>>>>>>> (This is related to the raspberry pi discussion in >>>>>>>> https://lore.kernel.org/qemu-devel/20250204002240.97830-1-philmd@linaro.org/). >>>>>>>> >>>>>>>> My plan is to deprecate 'petalogix-s3adsp1800', so once we >>>>>>>> remove it we can merge both qemu-system-microblaze and >>>>>>>> qemu-system-microblazeel into a single binary. >>>>>>>> >>>>>>>> If you don't want to add more machines, what should be the >>>>>>>> endianness of the 'petalogix-s3adsp1800' machine in a binary >>>>>>>> with no particular endianness? Either we add for explicit >>>>>>>> endianness (fixing test suites) or we add one machine for >>>>>>>> each endianness; I fail to see other options not too >>>>>>>> confusing for our users. >>>>>>> >>>>>>> We would pick an arbitrary endianness of our choosing >>>>>>> I guess. How does this work in physical machines ? Is >>>>>>> the choice of endianess a firmware setting, or a choice >>>>>>> by the vendor when manufacturing in some way ? >>>>>> >>>>>> Like MIPS*, SH4* and Xtensa*, it is a jumper on the board >>>>>> (wired to a CPU pin which is sampled once at cold reset). >>>>> >>>>> That makes me thing even more it is just a machine type property. >>>> >>>> I'm happy with a machine property, this was even my first approach >>>> using OnOffAuto until I ran the test-suite and have qom-introspection >>>> failing. >>>> >>>> What should be the default? >>>> >>>> Per the SH4 datasheet: >>>> >>>> Bit 31—Endian Flag (ENDIAN): Samples the value of the endian >>>> specification external pin (MD5) in a power-on reset by the >>>> RESET pin. The endian mode of all spaces is determined by this >>>> bit. ENDIAN is a read-only bit. >>>> >>>> There is no default per the spec, and I believe using one is >>>> a mistake. >>> >>> If it is left as an unspecified choice in the spec, then I would >>> presume HW vendors are picking an option based on what they >>> expect "most" common usage to be amongst their customers. IOW, >>> if we know of typically used guest OS prefer big or little, that >>> could influence our choice. >> >> Please have a look at this thread: >> https://lore.kernel.org/qemu-devel/d3346a55-584b-427b-8c87-32f7411a9290@amd.com/ > > That seems to give a pretty clear choice for qemu defaults > > "I am not aware about anybody configuring MB to big endian" > > so in that particular case, defaulting to LE would be most sensible. Or maybe I should stop trying to unify the current binaries, and add the new data-drive machines in a new binary, as you already suggested: https://lore.kernel.org/qemu-devel/ZEoyNt0UtSYRt9Go@redhat.com/ But then I'm worried about our users, on how to deprecate the current microblaze{,el} binaries to have them use the new one seamlessly. And more importantly, one of the goal is to maintain LESS binaries, no more.