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Tsirkin" To: David Woodhouse Cc: Richard Cochran , Peter Hilber , linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org, "Ridoux, Julien" , virtio-dev@lists.linux.dev, "Luu, Ryan" , "Chashper, David" , "Mohamed Abuelfotoh, Hazem" , "Christopher S . Hall" , Jason Wang , John Stultz , netdev@vger.kernel.org, Stephen Boyd , Thomas Gleixner , Xuan Zhuo , Marc Zyngier , Mark Rutland , Daniel Lezcano , Alessandro Zummo , Alexandre Belloni , qemu-devel , Simon Horman Subject: Re: [PATCH] ptp: Add vDSO-style vmclock support Message-ID: <20240725100351-mutt-send-email-mst@kernel.org> References: <14d1626bc9ddae9d8ad19d3c508538d10f5a8e44.camel@infradead.org> <20240725012730-mutt-send-email-mst@kernel.org> <7de7da1122e61f8c64bbaab04a35af93fafac454.camel@infradead.org> <20240725081502-mutt-send-email-mst@kernel.org> <20240725082828-mutt-send-email-mst@kernel.org> <20240725083215-mutt-send-email-mst@kernel.org> <98813a70f6d3377d3a9d502fd175be97334fcc87.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <98813a70f6d3377d3a9d502fd175be97334fcc87.camel@infradead.org> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.144, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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 Thu, Jul 25, 2024 at 02:50:50PM +0100, David Woodhouse wrote: > Even if the virtio-rtc specification were official today, and I was > able to expose it via PCI, I probably wouldn't do it that way. There's > just far more in virtio-rtc than we need; the simple shared memory > region is perfectly sufficient for most needs, and especially ours. I can't stop amazon from shipping whatever in its hypervisor, I'd just like to understand this better, if there is a use-case not addressed here then we can change virtio to address it. The rtc driver patch posted is 900 lines, yours is 700 lines, does not look like a big difference. As for using a memory region, this is valid, but maybe rtc should be changed to do exactly that? E.g. we can easily add a capability describing such a region. or put it in device config space. I mean yes, we can build a new transport for each specific need but in the end we'll get a ton of interfaces with unclear compatibility requirements. If effort is instead spent improving common interfaces, we get consistency and everyone benefits. That's why I'm trying to understand the need here. -- MST