linux-kernel - [PATCH 5/9] media: uvcvideo: Turn on the camera if V4L2_EVENT_SUB_FL_SEND

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Message-Id: <20250528-uvc-grannular-invert-v1-5-d01581f9cc25@chromium.org>
Date: Wed, 28 May 2025 17:58:00 +0000
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Hans de Goede <hdegoede@...hat.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Hans Verkuil <hverkuil@...all.nl>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH 5/9] media: uvcvideo: Turn on the camera if
 V4L2_EVENT_SUB_FL_SEND_INITIAL

If we subscribe to an event with V4L2_EVENT_SUB_FL_SEND_INITIAL, the
driver needs to report back some values that require the camera to be
powered on. But VIDIOC_SUBSCRIBE_EVENT is not part of the ioctls that
turn on the camera.

We could unconditionally turn on the camera during
VIDIOC_SUBSCRIBE_EVENT, but it is more efficient to turn it on only
during V4L2_EVENT_SUB_FL_SEND_INITIAL, which we believe is not a common
usecase.

Fixes: d1b618e79548 ("media: uvcvideo: Do not turn on the camera for some ioctls")
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
 drivers/media/usb/uvc/uvc_ctrl.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 44b6513c526421943bb9841fb53dc5f8e9f93f02..a7b8f3ea01edd8157e0d8cc36351d511225f89d7 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -2039,6 +2039,12 @@ static int uvc_ctrl_add_event(struct v4l2_subscribed_event *sev, unsigned elems)
 		u32 changes = V4L2_EVENT_CTRL_CH_FLAGS;
 		s32 val = 0;
 
+		ret = uvc_pm_get(handle->chain->dev);
+		if (ret) {
+			list_del(&sev->node);
+			goto done;
+		}
+
 		if (uvc_ctrl_mapping_is_compound(mapping) ||
 		    __uvc_ctrl_get(handle->chain, ctrl, mapping, &val) == 0)
 			changes |= V4L2_EVENT_CTRL_CH_VALUE;
@@ -2051,6 +2057,8 @@ static int uvc_ctrl_add_event(struct v4l2_subscribed_event *sev, unsigned elems)
 		 */
 		sev->elems = elems;
 		v4l2_event_queue_fh(sev->fh, &ev);
+
+		uvc_pm_put(handle->chain->dev);
 	}
 
 done:

-- 
2.49.0.1266.g31b7d2e469-goog