Message-ID: <ZIL5LcXFCzWM9qtM@tom-HP-ZBook-Fury-15-G7-Mobile-Workstation>
Date:   Fri, 9 Jun 2023 12:04:29 +0200
From:   Tommaso Merciai <tomm.merciai@...il.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     jacopo.mondi@...asonboard.com, laurent.pinchart@...asonboard.com,
        martin.hecht@...et.eu, michael.roeder@...et.eu,
        linuxfancy@...glegroups.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Gerald Loacker <gerald.loacker@...fvision.net>,
        Shawn Tu <shawnx.tu@...el.com>,
        Krzysztof Hałasa <khalasa@...p.pl>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nicholas Roth <nicholas@...hemail.net>,
        Mikhail Rudenko <mike.rudenko@...il.com>,
        Benjamin Mugnier <benjamin.mugnier@...s.st.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/3] media: dt-bindings: alvium: add document YAML
 binding

Hi Sakari,

On Fri, Jun 09, 2023 at 09:44:18AM +0000, Sakari Ailus wrote:
> Hi Tommaso,
> 
> On Fri, Jun 09, 2023 at 11:41:16AM +0200, Tommaso Merciai wrote:
> > Hi Sakari,
> > Thanks for your feedback.
> > 
> > On Fri, Jun 09, 2023 at 08:35:20AM +0000, Sakari Ailus wrote:
> > > Hi Tommaso,
> > > 
> > > On Thu, Jun 08, 2023 at 10:31:15AM +0200, Tommaso Merciai wrote:
> > > > Add documentation of device tree in YAML schema for the ALVIUM
> > > > Camera from Allied Vision Inc.
> > > > 
> > > > References:
> > > >  - https://www.alliedvision.com/en/products/embedded-vision-solutions
> > > > 
> > > > Signed-off-by: Tommaso Merciai <tomm.merciai@...il.com>
> > > > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > > > ---
> > > > Changes since v1:
> > > >  - Fixed build error as suggested by RHerring bot
> > > > 
> > > > Changes since v2:
> > > >  - Fixed License as suggested by KKozlowski/CDooley
> > > >  - Removed rotation property as suggested by CDooley/LPinchart
> > > >  - Fixed example node name as suggested by CDooley
> > > >  - Fixed title as suggested by LPinchart
> > > >  - Fixed compatible name as suggested by LPinchart
> > > >  - Removed clock as suggested by LPinchart
> > > >  - Removed gpios not as suggested by LPinchart
> > > >  - Renamed property name streamon-delay into alliedvision,lp2hs-delay-us
> > > >  - Fixed vendor prefix, unit append as suggested by KKozlowski
> > > >  - Fixed data-lanes
> > > >  - Fixed blank space + example indentation (from 6 -> 4 space) as suggested by KKozlowski
> > > >  - Dropped status into example  as suggested by KKozlowski
> > > >  - Added vcc-ext-in supply as suggested by LPinchart
> > > >  - Dropped pinctrl into example as suggested by LPinchart
> > > > 
> > > > Changes since v3:
> > > >  - Fixed vcc-ext-in-supply description as suggested by LPinchart
> > > >  - Fixed alliedvision,lp2hs-delay-us description as suggested by LPinchart
> > > >  - Added maximum to alliedvision,lp2hs-delay-us as suggested by LPinchart
> > > >  - Collected Reviewed-by tag from LPinchart
> > > > 
> > > > Changes since v4:
> > > >  - Fixed id as reported by RHerring bot and LPinchart
> > > >  - Add minimum into alliedvision,lp2hs-delay-us as suggested by CDooley
> > > >  - Tested using make dt_binding_check DT_SCHEMA_FILES=alliedvision,alvium-csi2.yaml
> > > > 
> > > >  .../media/i2c/alliedvision,alvium-csi2.yaml   | 97 +++++++++++++++++++
> > > >  1 file changed, 97 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/media/i2c/alliedvision,alvium-csi2.yaml
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/media/i2c/alliedvision,alvium-csi2.yaml b/Documentation/devicetree/bindings/media/i2c/alliedvision,alvium-csi2.yaml
> > > > new file mode 100644
> > > > index 000000000000..c771e5039641
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/media/i2c/alliedvision,alvium-csi2.yaml
> > > > @@ -0,0 +1,97 @@
> > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/media/i2c/alliedvision,alvium-csi2.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Allied Vision Alvium Camera
> > > > +
> > > > +maintainers:
> > > > +  - Tommaso Merciai <tomm.merciai@...il.com>
> > > > +  - Martin Hecht <martin.hecht@...et.eu>
> > > > +
> > > > +allOf:
> > > > +  - $ref: /schemas/media/video-interface-devices.yaml#
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    const: alliedvision,alvium-csi2
> > > > +
> > > > +  reg:
> > > > +    maxItems: 1
> > > > +
> > > > +  vcc-ext-in-supply:
> > > > +    description: |
> > > > +      The regulator that supplies power to the VCC_EXT_IN pins.
> > > > +
> > > > +  alliedvision,lp2hs-delay-us:
> > > > +    minimum: 1
> > > > +    maximum: 150000
> > > > +    description: |
> > > > +      Low power to high speed delay time.
> > > > +
> > > > +      If the value is larger than 0, the camera forces a reset of all
> > > > +      D-PHY lanes for the duration specified by this property. All lanes
> > > > +      will transition to the low-power state and back to the high-speed
> > > > +      state after the delay. Otherwise the lanes will transition to and
> > > > +      remain in the high-speed state immediately after power on.
> > > > +
> > > > +      This is meant to help CSI-2 receivers synchronizing their D-PHY
> > > > +      RX.
> > > 
> > > Why do you need this? D-PHY TX is obviously controlled by the driver.
> > > Explicit control of PHY initialisation is of course best option when
> > > combined with some receivers, done via driver's pre_streamon and s_stream
> > > callbacks. Can't your hardware do that?
> > 
> > You mean calculate this time in some dynamical way and program this
> > during pre_streamon or s_stream?
> > 
> > If yes, unfortunately hw can't do this.
> 
> This shouldn't be based on timing but rather progress of the bus
> initialisation sequence. That's how it works on most sensors nowadays.

Just to clarify, this is not a sensor:

"The Alvium camera is shipped with sensor + isp in the same housing.
The camera can be equipped with one out of various sensor and abstract
the user from this. Camera is connected via MIPI CSI-2."

> 
> The description is also lacking details on what delay this exactly is. What
> is the bus state during that delay?

Previously we have a brief thread with Laurent about
the behaviour of this reg/property, I repost here:

"Thanks to Martin Hecht I'm able to provide you a clearer description:

Alvium normally delivers a continous clock even when it is not streaming.
The purpose of this reg is force a DPhy reset for the period described by
the us on the reg before it starts streaming. To be clear, with that value
bigger than 0 the Alvium forces a dphy-reset on all lanes for that period.
That means all lanes go up into low power state.
This may help a csi2 rx ip to reset if that IP can't deal with a continous clock."


Hope these infos can clarify.
Let me know.

Thanks,
Tommaso

> 
> -- 
> Regards,
> 
> Sakari Ailus

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