RE: [PATCH v2 6/7] dt-bindings: media: Add Renesas R-Car DRIF binding

[Chris Paterson <Chris.Paterson2@renesas.com>]

Hello Hans,

Do you have any further feedback on this?

Thanks, Chris


> From: Ramesh Shanmugasundaram
> Sent: 10 January 2017 09:31
> Hi Laurent,
> 
> > > >>> On Wednesday 21 Dec 2016 08:10:37 Ramesh Shanmugasundaram
> wrote:
> > > >>>> Add binding documentation for Renesas R-Car Digital Radio
> > > >>>> Interface
> > > >>>> (DRIF) controller.
> > > >>>>
> > > >>>> Signed-off-by: Ramesh Shanmugasundaram
> > > >>>> <ramesh.shanmugasundaram@bp.renesas.com> ---
> > > >>>>
> > > >>>>  .../devicetree/bindings/media/renesas,drif.txt     | 202
> > +++++++++++++
> > > >>>>  1 file changed, 202 insertions(+)  create mode 100644
> > > >>>>
> > > >>>> Documentation/devicetree/bindings/media/renesas,drif.txt
> > > >>>>
> > > >>>> diff --git
> > > >>>> a/Documentation/devicetree/bindings/media/renesas,drif.txt
> > > >>>> b/Documentation/devicetree/bindings/media/renesas,drif.txt new
> > > >>>> file mode 100644 index 0000000..1f3feaf
> > > >>>> --- /dev/null
> > > >>>> +++ b/Documentation/devicetree/bindings/media/renesas,drif.txt
> > > >>>>
> > > >>>> +Optional properties of an internal channel when:
> > > >>>> +     - It is the only enabled channel of the bond (or)
> > > >>>> +     - If it acts as primary among enabled bonds
> > > >>>> +--------------------------------------------------------
> > > >>>> +- renesas,syncmd       : sync mode
> > > >>>> +                      0 (Frame start sync pulse mode. 1-bit
> > > >>>> +width
> > > >>>> pulse
> > > >>>> +                         indicates start of a frame)
> > > >>>> +                      1 (L/R sync or I2S mode) (default)
> > > >>>> +- renesas,lsb-first    : empty property indicates lsb bit is
> > received
> > > >>>> first.
> > > >>>> +                      When not defined msb bit is received
> > > >>>> +first
> > > >>>> +(default)
> > > >>>> +- renesas,syncac-active: Indicates sync signal polarity, 0/1
> > > >>>> +for
> > > >>>> low/high
> > >
> > > Shouldn't this be 'renesas,sync-active' instead of syncac-active?
> > >
> > > I'm not sure if syncac is intended or if it is a typo.
> > >
> > > >>>> +                      respectively. The default is 1 (active high)
> > > >>>> +- renesas,dtdl         : delay between sync signal and start of
> > > >>>> reception.
> > > >>>> +                      The possible values are represented in
> > > >>>> + 0.5
> > clock
> > > >>>> +                      cycle units and the range is 0 to 4. The
> > default
> > > >>>> +                      value is 2 (i.e.) 1 clock cycle delay.
> > > >>>> +- renesas,syncdl       : delay between end of reception and sync
> > > >>>> signal edge.
> > > >>>> +                      The possible values are represented in
> > > >>>> + 0.5
> > clock
> > > >>>> +                      cycle units and the range is 0 to 4 & 6.
> > > >>>> + The
> > > >>>> default
> > > >>>> +                      value is 0 (i.e.) no delay.
> > > >>>
> > > >>> Most of these properties are pretty similar to the video bus
> > > >>> properties defined at the endpoint level in
> > > >>> Documentation/devicetree/bindings/media/video-interfaces.txt. I
> > > >>> believe it would make sense to use OF graph and try to
> > > >>> standardize these properties similarly.
> > >
> > > Other than sync-active, is there really anything else that is similar?
> > > And even the sync-active isn't a good fit since here there is only
> > > one sync signal instead of two for video (h and vsync).
> >
> > That's why I said similar, not identical :-) My point is that, if we
> > consider that we could connect multiple sources to the DRIF, using OF
> > graph would make sense, and the above properties should then be
> > defined per endpoint.
> 
> Thanks for the clarifications. I have some questions.
> 
> - Assuming two devices are interfaced with DRIF and they are represented
> using two endpoints, the control signal related properties of DRIF might still
> need to be same for both endpoints? For e.g. syncac-active cannot be
> different in both endpoints?
> 
> - I suppose "lsb-first", "dtdl" & "syncdl" may be defined per endpoint.
> However, h/w manual says same register values needs to be programmed
> for both the internal channels of a channel. Same with "syncmd" property.
> 
> We could still define them as per endpoint property with a note that they
> need to be same. But I am not sure if that is what you intended?
> 
>  If we define them per endpoint we should then also try
> > standardize the ones that are not really Renesas-specific (that's at
> > least syncac-active).
> 
> OK. I will call it "sync-active".
> 
>  For the syncmd and lsb-first properties, it could also
> > make sense to query them from the connected subdev at runtime, as
> > they're similar in purpose to formats and media bus configuration
> > (struct v4l2_mbus_config).
> 
> May I know in bit more detail about what you had in mind? Please correct me
> if my understanding is wrong here but when I looked at the code
> 
> 1) mbus_config is part of subdev_video_ops only. I assume we don't want to
> support this as part of tuner subdev. The next closest is pad_ops with "struct
> v4l2_mbus_framefmt" but it is fully video specific config unless I come up
> with new MEDIA_BUS_FMT_xxxx in media-bus-format.h and use the code
> field? For e.g.
> 
> #define MEDIA_BUS_FMT_SDR_I2S_PADHI_BE       0x7001
> #define MEDIA_BUS_FMT_SDR_I2S_PADHI_LE       0x7002
> 
> 2) The framework does not seem to mandate pad ops for all subdev. As the
> tuner can be any third party subdev, is it fair to assume that these properties
> can be queried from subdev?
> 
> 3) Assuming pad ops is not available on the subdev shouldn't we still need a
> way to define these properties on DRIF DT?
> 
> >
> > I'm not an SDR expert, so I'd like to have your opinion on this.
> >
> > > >> Note that the last two properties match the those in
> > > >> Documentation/devicetree/bindings/spi/sh-msiof.txt.
> > > >> We may want to use one DRIF channel as a plain SPI slave with the
> > > >> (modified) MSIOF driver in the future.
> > > >
> > > > Should I leave it as it is or modify these as in video-interfaces.txt?
> > > > Shall we conclude on this please?
> >
> 
> Thanks,
> Ramesh