Date:   Tue, 7 Mar 2023 08:17:04 +0000
From:   "Wu, Wentong" <wentong.wu@...el.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
CC:     "mchehab@...nel.org" <mchehab@...nel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>,
        "pierre-louis.bossart@...ux.intel.com" 
        <pierre-louis.bossart@...ux.intel.com>,
        "Wang, Zhifeng" <zhifeng.wang@...el.com>,
        "Ye, Xiang" <xiang.ye@...el.com>,
        "Qiu, Tian Shu" <tian.shu.qiu@...el.com>,
        "Cao, Bingbu" <bingbu.cao@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 0/3] media: pci: intel: ivsc: Add driver of Intel
 Visual Sensing Controller(IVSC)



> -----Original Message-----
> From: Hans de Goede <hdegoede@...hat.com>
> 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.

Thanks
Wentong

> 
> Regards,
> 
> Hans
> 
> 
> 
> >
> > - The CSI-2 configuration should take place when streaming starts on the
> >   sensor (as well as IVSC).
> >
> > - Device links need to be set up via IPU bridge which now is called  CIO2
> >   bridge (cio2-bridge.c).
> >
> > Any questions, comments?
> >

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