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Tsirkin" , Eugenio =?utf-8?Q?P=C3=A9rez?= , Manos Pitsidianakis , devel@lists.libvirt.org, Richard Henderson , Peter Maydell , qemu-arm@nongnu.org, Jason Wang Subject: Re: [PATCH] hw/arm: Deprecate legacy VirtIO devices on big-endian guests In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Wed, 17 Dec 2025 14:26:07 +0000") References: <20251217140658.89715-1-philmd@linaro.org> User-Agent: mu4e 1.12.14-pre3; emacs 30.1 Date: Wed, 17 Dec 2025 17:13:04 +0000 Message-ID: <8734592frz.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::42c; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x42c.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-arm@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-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > On Wed, Dec 17, 2025 at 03:06:57PM +0100, Philippe Mathieu-Daud=C3=A9 wro= te: >> We couldn't find a way (guest OS with VirtIO drivers) to test >> a legacy VirtIO device on a ARM vCPU running in big-endian. >>=20 >> Deprecate for the v11.0 release, giving 1 year to users who >> really care to contribute functional tests. >>=20 >> Suggested-by: Alex Benn=C3=A9e >> Signed-off-by: Philippe Mathieu-Daud=C3=A9 >> --- >> docs/about/deprecated.rst | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >>=20 >> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst >> index ac31a2bce42..3a69facb0f1 100644 >> --- a/docs/about/deprecated.rst >> +++ b/docs/about/deprecated.rst >> @@ -515,6 +515,17 @@ It was implemented as a no-op instruction in TCG up= to QEMU 9.0, but >> only with ``-cpu max`` (which does not guarantee migration compatibility >> across versions). >>=20=20 >> +VirtIO devices >> +'''''''''''''' >> + >> +Legacy VirtIO devices on Big-Endian ARM architecture (since 11.0) >> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >> + >> +There are no functional tests for legacy virtio devices used by ARM >> +machines running in big-endian order, which makes harder to maintain >> +the code path while the code base evolve. > > Lack of test coverage is not a reason to deprecate something. > > We deprecate things we intend to intentionally remove or intentionally > change in an incompatible manner. We also deprecate things that stop us moving the code forward. c.f. the long process to deprecate 32 bit hosts. > If something is not tested, that merely means it has lesser quality > guarantees, and is liable to unintenionally get broken at times. > > If we're planning to *intentionally* remove the ability to use > legacy virtio on big endian, that would be a reason to deprecate. > If so the deprecation message should say this, not talk about > missing functional testing. As far as I'm aware BE Arm is a very small niche and I'm not even sure anyone runs BE Arm systems with VirtIO - let alone legacy VirtIO. If there are people that need this functionality they need to at least make themselves known. --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro