Hi Wentong, On Tue, Mar 07, 2023 at 08:17:04AM +0000, Wu, Wentong wrote: > > > > -----Original Message----- > > From: Hans de Goede <hdegoede@xxxxxxxxxx> > > Sent: Wednesday, March 1, 2023 6:42 PM > > > > Hi, > > > > On 3/1/23 11:34, Sakari Ailus wrote: > > > Hi Wentong, > > > > > > On Mon, Feb 13, 2023 at 10:23:44AM +0800, Wentong Wu wrote: > > >> Intel Visual Sensing Controller (IVSC), codenamed "Clover Falls", is > > >> a companion chip designed to provide secure and low power vision > > >> capability to IA platforms. IVSC is available in existing commercial > > >> platforms from multiple OEMs. > > >> > > >> The primary use case of IVSC is to bring in context awareness. IVSC > > >> interfaces directly with the platform main camera sensor via a CSI-2 > > >> link and processes the image data with the embedded AI engine. The > > >> detected events are sent over I2C to ISH (Intel Sensor Hub) for > > >> additional data fusion from multiple sensors. The fusion results are > > >> used to implement advanced use cases like: > > >> - Face detection to unlock screen > > >> - Detect user presence to manage backlight setting or waking up > > >> system > > >> > > >> Since the Image Processing Unit(IPU) used on the host processor needs > > >> to configure the CSI-2 link in normal camera usages, the CSI-2 link > > >> and camera sensor can only be used in mutually-exclusive ways by host > > >> IPU and IVSC. By default the IVSC owns the CSI-2 link and camera > > >> sensor. The IPU driver can take ownership of the CSI-2 link and > > >> camera sensor using interfaces provided by this IVSC driver. > > >> > > >> Switching ownership requires an interface with two different hardware > > >> modules inside IVSC. The software interface to these modules is via > > >> Intel MEI (The Intel Management Engine) commands. These two hardware > > >> modules have two different MEI UUIDs to enumerate. These hardware > > modules are: > > >> - ACE (Algorithm Context Engine): This module is for algorithm > > >> computing when IVSC owns camera sensor. Also ACE module controls > > >> camera sensor's ownership. This hardware module is used to set ownership > > of camera sensor. > > >> - CSI (Camera Serial Interface): This module is used to route camera > > >> sensor data either to IVSC or to host for IPU driver and application. > > >> > > >> IVSC also provides a privacy mode. When privacy mode is turned on, > > >> camera sensor can't be used. This means that both ACE and host IPU > > >> can't get image data. And when this mode is turned on, host IPU > > >> driver is informed via a registered callback, so that user can be notified. > > >> > > >> In summary, to acquire ownership of camera by IPU driver, first ACE > > >> module needs to be informed of ownership and then to setup MIPI CSI-2 > > >> link for the camera sensor and IPU. > > > > > > I thought this for a while and did some research, and I can suggest > > > the > > > following: > > > > > > - The IVSC sub-device implements a control for privacy (V4L2_CID_PRIVACY > > > is a good fit). > > > > > > - Camera sensor access needs to be requested from IVSC before accessing the > > > sensor via I²C. The IVSC ownership control needs to be in the right > > > setting for this to work, and device links can be used for that purpose > > > (see device_link_add()). With DL_FLAG_PM_RUNTIME and > > DL_FLAG_RPM_ACTIVE, > > > the supplier devices will be PM runtime resumed before the consumer > > > (camera sensor). As these devices are purely virtual on host side and has > > > no power state as such, you can use runtime PM callbacks to transfer the > > > ownership. > > > > Interesting proposal to use device-links + runtime-pm for this instead of > > modelling this as an i2c-mux. FWIW I'm fine with going this route instead of > > using an i2c-mux approach. > > > > I have been thinking about the i2c-mux approach a bit and the problem is that > > we are not really muxing but want to turn on/off control and AFAIK the i2c-mux > > framework simply leaves the mux muxed to the last used i2c-chain, so control > > will never be released when the i2c transfers are done. > > > > And if were to somehow modify things (or maybe there already is some release > > callback) then the downside becomes that the i2c-mux core code operates at > > the i2c transfer level. So each i2c read/write would then enable + disavle control. > > > > Modelling this using something like runtime pm as such is a much better fit > > because then we request control once on probe / stream-on and release it once > > we are fully done, rather then requesting + releasing control once per i2c- > > transfer. > > Seems runtime pm can't fix the problem of initial i2c transfer during sensor driver probe, > probably we have to switch to i2c-mux modeling way. What do you mean? The supplier devices are resumed before the driver's probe is called. -- Regards, Sakari Ailus
