On 8/14/20 12:11 PM, Bingbu Cao wrote: > > > On 8/10/20 10:27 PM, Sakari Ailus wrote: >> Hi all, >> > ...snip... >> >> The use case is such that there is a privacy LED next to an integrated >> user-facing laptop camera, and this LED is there to signal the user that >> the camera is recording a video or capturing images. That LED also happens >> to be wired to one of the power supplies of the camera, so whenever you >> power on the camera, the LED will be lit, whether images are captured from >> the camera --- or not. There's no way to implement this differently >> without additional software control (allowing of which is itself a >> hardware design decision) on most CSI-2-connected camera sensors as they >> simply have no pin to signal the camera streaming state. >> >> This is also what happens during driver probe: the camera will be powered >> on by the I²C subsystem calling dev_pm_domain_attach() and the device is >> already powered on when the driver's own probe function is called. To the >> user this visible during the boot process as a blink of the privacy LED, >> suggesting that the camera is recording without the user having used an >> application to do that. From the end user's point of view the behaviour is >> not expected and for someone unfamiliar with internal workings of a >> computer surely seems quite suspicious --- even if images are not being >> actually captured. >> >> I've tested these on linux-next master. They also apply to Wolfram's >> i2c/for-next branch, there's a patch that affects the I²C core changes >> here (see below). The patches apart from that apply to Bartosz's >> at24/for-next as well as Mauro's linux-media master branch. > > Sakari, we meet one issue - once the vcm sub-device registered, the user space > will try to open the VCM (I have not figure out who did that), it will also > trigger the acpi pm resume/suspend, as the VCM always shares same power rail > with camera sensor, so the privacy LED still has a blink. Sakari, please ignore my previous comment, it is not related to this change. I see the sub device open is caused by v4l_id program from udev. > >> > ...snip... > -- Best regards, Bingbu Cao
