Date:   Fri, 17 Feb 2023 12:49:34 +0200
From:   Sakari Ailus <sakari.ailus@linux.intel.com>
To:     "Wu, Wentong" <wentong.wu@intel.com>
Cc:     Bingbu Cao <bingbu.cao@linux.intel.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        "mchehab@kernel.org" <mchehab@kernel.org>,
        "linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
        "Pandruvada, Srinivas" <srinivas.pandruvada@intel.com>,
        "pierre-louis.bossart@linux.intel.com" 
        <pierre-louis.bossart@linux.intel.com>,
        "Wang, Zhifeng" <zhifeng.wang@intel.com>,
        "Ye, Xiang" <xiang.ye@intel.com>,
        "Qiu, Tian Shu" <tian.shu.qiu@intel.com>,
        "Cao, Bingbu" <bingbu.cao@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 0/3] media: pci: intel: ivsc: Add driver of Intel
 Visual Sensing Controller(IVSC)
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Hi Wentong,

On Fri, Feb 17, 2023 at 06:28:32AM +0000, Wu, Wentong wrote:
> 
> 
> > -----Original Message-----
> > From: Bingbu Cao <bingbu.cao@linux.intel.com>
> > Sent: Friday, February 17, 2023 9:44 AM
> > 
> > Hi, Sakari,
> > 
> > On 2/16/23 9:12 PM, Sakari Ailus wrote:
> > > Hi Bingbu, Wentong,
> > >
> > > On Wed, Feb 15, 2023 at 08:09:50PM +0800, Bingbu Cao wrote:
> > >>
> > >> Hi, Wentong,
> > >>
> > >> On 2/15/23 5:43 PM, Laurent Pinchart wrote:
> > >>> Hello 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
> > >>>
> > >>> Do you have plan to support these features in the ivsc driver in the
> > >>> future ?
> > >>>
> > >>>> 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.
> > >>>
> > >>> How does the privacy mode work, and how can the user trust that the
> > >>> closed-source IVSC and IME firmwares will honour the privacy settings ?
> > 
> > As I know, without IVSC, once user enable the privacy mode, the Intel
> > Converged Security Engine will configure the IPU camera mask (security register),
> > which will mask the specific CSI2 port and produce dummy imaging data. For the
> > case with IVSC, there is no final solution on Linux so far I think.
> > 
> > Wentong, is IVSC trying to cut off the stream and then notify user and IPU?
> 
> yes

Does the CSI-2 transmitter on IVCS go to some LP mode during this time, or
does the receiver need to initialise the bus again when the stream resuems?

> 
> > 
> > >>>
> > >>
> > >> Continue with question from Laurent,
> > >>
> > >> How IVSC handle the privacy request from user? Is there some
> > >> notification mechanism to user-space?
> 
> IVSC has already defined privacy callback for host IPU/camera driver.
> 
> > > I'd have concern if IVSC driver
> > >> need private callback to request back-end(e.g. ISP driver) to handle stream
> > cutting.
> > >
> > > How does the privacy mode work, does it just pass zeroes (or other
> > > dummy
> > > data) towards the host or nothing?
> 
> No data on CSI transmitter side

Can it stop in the middle of the frame? Or is it guaranteed to produce full
frames (assuming the sensor does)?

> 
> > >
> > > A V4L2 control can be used for the purpose of passing the information
> > > to the user space at least.
> 
> I will take some time to review V4L2 sub-device and control mechanism,
> and then update the driver.

-- 
Kind regards,

Sakari Ailus