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([38.81.85.65]) by smtp.gmail.com with ESMTPSA id 00721157ae682-85e6756e0f3sm8064327b3.43.2026.08.28.08.26.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2026 08:26:01 -0700 (PDT) From: Michael Jordan To: Laurent Pinchart , Hans de Goede , Ricardo Ribalda Cc: Mauro Carvalho Chehab , Hans Verkuil , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, Michael Jordan Subject: [PATCH 1/3] media: uvcvideo: report AUTO_UPDATE controls as volatile Date: Fri, 28 Aug 2026 11:25:55 -0400 Message-ID: <20260828152557.653475-2-jordan.mymail@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260828152557.653475-1-jordan.mymail@gmail.com> References: <20260828152557.653475-1-jordan.mymail@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A control with UVC_CTRL_FLAG_AUTO_UPDATE is one whose value the device changes on its own: the driver never trusts its cached value for it, re-reading the device on every VIDIOC_G_EXT_CTRLS (the rollback at the end of the ioctl runs uvc_ctrl_commit_entity(), which clears ctrl->loaded for these controls) and re-reading it after each write. That is exactly what V4L2_CTRL_FLAG_VOLATILE describes to userspace, but the driver never reported it, so applications had no way to know that the value they read can change under them and that a fresh read is worth issuing. Report V4L2_CTRL_FLAG_VOLATILE for AUTO_UPDATE controls. The uAPI documents writes to a volatile control as ignored unless V4L2_CTRL_FLAG_EXECUTE_ON_WRITE is also set, and this driver sends every write of a writable control to the device, so report EXECUTE_ON_WRITE alongside it whenever the control is settable. Suggested-by: Ricardo Ribalda Signed-off-by: Michael Jordan --- drivers/media/usb/uvc/uvc_ctrl.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c index 3ca108b83..aceb26310 100644 --- a/drivers/media/usb/uvc/uvc_ctrl.c +++ b/drivers/media/usb/uvc/uvc_ctrl.c @@ -1840,6 +1840,17 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain, if ((ctrl->info.flags & UVC_CTRL_FLAG_GET_MAX) && (ctrl->info.flags & UVC_CTRL_FLAG_GET_MIN)) v4l2_ctrl->flags |= V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX; + if (ctrl->info.flags & UVC_CTRL_FLAG_AUTO_UPDATE) { + v4l2_ctrl->flags |= V4L2_CTRL_FLAG_VOLATILE; + /* + * Writes to a volatile control are documented to be ignored + * unless EXECUTE_ON_WRITE is also reported. The driver sends + * every write of a writable control to the device, so report + * the flag accordingly. + */ + if (ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR) + v4l2_ctrl->flags |= V4L2_CTRL_FLAG_EXECUTE_ON_WRITE; + } if (mapping->master_id) __uvc_find_control(ctrl->entity, mapping->master_id, -- 2.43.0