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Fri, 02 Oct 2026 05:41:06 -0700 (PDT) From: Michael Jordan To: Hans Verkuil Cc: Michael Jordan , Laurent Pinchart , Hans de Goede , Hans de Goede , Ricardo Ribalda , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/4] media: uvcvideo: report AUTO_UPDATE controls as volatile Date: Fri, 2 Oct 2026 08:41:05 -0400 Message-ID: <20261002124105.55173-1-jordan.mymail@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <60efdb3c-e669-403d-b2d5-fee993e16217@kernel.org> References: <20260928215021.819064-1-jordan.mymail@gmail.com> <20260928215021.819064-2-jordan.mymail@gmail.com> <20260929123422.GA349401@killaraus.ideasonboard.com> <60efdb3c-e669-403d-b2d5-fee993e16217@kernel.org> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Hans, Thanks for pointing me to `v4l2_ctrl_auto_cluster()`. I’m trying to understand how to apply that model correctly here. >From UVC 1.5 §4.1.2, Table 4-3, I understand that GET_INFO distinguishes “Disabled due to automatic mode” (D2, a state bit) from “Autoupdate Control” (D3, a capability bit). That helps me understand why AUTO_UPDATE alone should not determine the flags for controls with an auto/manual master. The Tiny 2 and Tail 2 pan/tilt case is what I’m unsure about. These are the only cameras I have available to test. On both, writing the V4L2 pan/tilt controls sends a target position to the camera. With the AUTO_UPDATE fixups applied, subsequent V4L2 reads retrieve values from the camera that follow its movement towards that target, rather than immediately returning the commanded target. I observed this with tracking disabled as well. The pan/tilt mappings in uvcvideo have no `master_id`. This is what I observed on these devices; I’m not assuming the specification requires live position feedback. In particular, §4.2.2.1.14 describes pan/tilt “settings,” and both cameras advertise UVC 1.00. Would the appropriate approach be to follow the mode-dependent flag handling you described for controls with an auto/manual master, and use `VOLATILE | EXECUTE_ON_WRITE` for writable PTZ controls exhibiting this behavior? Or am I misunderstanding how that read/write behavior should be represented in V4L2? The v5 I sent fixes the event-notification issue but retains the blanket flag mapping, so your feedback still applies. Thanks for helping me understand this. Michael