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Date:   Tue, 18 Jun 2019 12:45:08 +0000
From:   Vishal Sagar <vsagar@...inx.com>
To:     Hans Verkuil <hverkuil@...all.nl>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Dinesh Kumar <dineshk@...inx.com>,
        Sandip Kothari <sandipk@...inx.com>,
        Vishal Sagar <vishal.sagar@...inx.com>,
        Hyun Kwon <hyunk@...inx.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michal Simek <michals@...inx.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: RE: [PATCH 2/2] media: v4l: xilinx: Add Xilinx UHD-SDI Rx Subsystem
 driver


Hi Hans,

> -----Original Message-----
> From: Hans Verkuil [mailto:hverkuil@...all.nl]
> Sent: Tuesday, June 18, 2019 5:38 PM
> To: Vishal Sagar <vsagar@...inx.com>
> Cc: linux-kernel@...r.kernel.org; linux-media@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; devicetree@...r.kernel.org; Dinesh Kumar
> <dineshk@...inx.com>; Sandip Kothari <sandipk@...inx.com>; Vishal Sagar
> <vishal.sagar@...inx.com>; Hyun Kwon <hyunk@...inx.com>; Laurent Pinchart
> <laurent.pinchart@...asonboard.com>; Mauro Carvalho Chehab
> <mchehab@...nel.org>; Michal Simek <michals@...inx.com>; Rob Herring
> <robh+dt@...nel.org>; Mark Rutland <mark.rutland@....com>; Sakari Ailus
> <sakari.ailus@...ux.intel.com>
> Subject: Re: [PATCH 2/2] media: v4l: xilinx: Add Xilinx UHD-SDI Rx Subsystem
> driver
> 
> On 6/18/19 1:51 PM, Vishal Sagar wrote:
> > Hi Hans,
> >
> >> -----Original Message-----
> >> From: Hans Verkuil [mailto:hverkuil@...all.nl]
> >> Sent: Saturday, June 15, 2019 1:25 PM
> >> To: Vishal Sagar <vsagar@...inx.com>
> >> Cc: linux-kernel@...r.kernel.org; linux-media@...r.kernel.org; linux-arm-
> >> kernel@...ts.infradead.org; devicetree@...r.kernel.org; Dinesh Kumar
> >> <dineshk@...inx.com>; Sandip Kothari <sandipk@...inx.com>; Vishal Sagar
> >> <vishal.sagar@...inx.com>; Hyun Kwon <hyunk@...inx.com>; Laurent
> Pinchart
> >> <laurent.pinchart@...asonboard.com>; Mauro Carvalho Chehab
> >> <mchehab@...nel.org>; Michal Simek <michals@...inx.com>; Rob Herring
> >> <robh+dt@...nel.org>; Mark Rutland <mark.rutland@....com>; Sakari
> Ailus
> >> <sakari.ailus@...ux.intel.com>
> >> Subject: Re: [PATCH 2/2] media: v4l: xilinx: Add Xilinx UHD-SDI Rx Subsystem
> >> driver
> >>
> >> On 6/14/19 1:44 PM, Vishal Sagar wrote:
> >>> Hi Hans,
> >>>
> >>> Thanks for reviewing this patch.
> >>>
> >>>> -----Original Message-----
> >>>> From: Hans Verkuil [mailto:hverkuil@...all.nl]
> >>>> Sent: Wednesday, June 05, 2019 6:28 PM
> >>>> To: Vishal Sagar <vishal.sagar@...inx.com>; Hyun Kwon
> >> <hyunk@...inx.com>;
> >>>> Laurent Pinchart <laurent.pinchart@...asonboard.com>; Mauro Carvalho
> >>>> Chehab <mchehab@...nel.org>; Michal Simek <michals@...inx.com>;
> Rob
> >>>> Herring <robh+dt@...nel.org>; Mark Rutland <mark.rutland@....com>
> >>>> Cc: linux-kernel@...r.kernel.org; linux-media@...r.kernel.org; linux-arm-
> >>>> kernel@...ts.infradead.org; devicetree@...r.kernel.org; Dinesh Kumar
> >>>> <dineshk@...inx.com>; Sandip Kothari <sandipk@...inx.com>
> >>>> Subject: Re: [PATCH 2/2] media: v4l: xilinx: Add Xilinx UHD-SDI Rx
> Subsystem
> >>>> driver
> >>>>
> >>>> EXTERNAL EMAIL
> >>>>
> >>>> On 6/4/19 3:55 PM, Vishal Sagar wrote:
> >>>>> The Xilinx UHD-SDI Rx subsystem soft IP is used to capture native SDI
> >>>>> streams from SDI sources like SDI broadcast equipment like cameras and
> >>>>> mixers. This block outputs either native SDI, native video or
> >>>>> AXI4-Stream compliant data stream for further processing. Please refer
> >>>>> to PG290 for details.
> >>>>>
> >>>>> The driver is used to configure the IP to add framer, search for
> >>>>> specific modes, get the detected mode, stream parameters, errors, etc.
> >>>>> It also generates events for video lock/unlock, bridge over/under flow.
> >>>>>
> >>>>> The driver supports only 10 bpc YUV 422 media bus format. It also
> >>>>> decodes the stream parameters based on the ST352 packet embedded in
> >> the
> >>>>> stream. In case the ST352 packet isn't present in the stream, the core's
> >>>>> detected properties are used to set stream properties.
> >>>>>
> >>>>> The driver currently supports only the AXI4-Stream configuration.
> >>>>>
> >>>>> Signed-off-by: Vishal Sagar <vishal.sagar@...inx.com>
> >>>>> ---
> >>>>>  drivers/media/platform/xilinx/Kconfig          |   11 +
> >>>>>  drivers/media/platform/xilinx/Makefile         |    1 +
> >>>>>  drivers/media/platform/xilinx/xilinx-sdirxss.c | 1846
> >>>> ++++++++++++++++++++++++
> >>>>>  include/uapi/linux/xilinx-sdirxss.h            |   63 +
> >>>>>  include/uapi/linux/xilinx-v4l2-controls.h      |   30 +
> >>>>>  include/uapi/linux/xilinx-v4l2-events.h        |    9 +
> >>
> >> <snip>
> >>
> >>>> I am concerned about this driver: I see that none of the *_dv_timings
> >> callbacks
> >>>> are implemented. I would expect to see that for a video receiver. There is
> >> also
> >>>> no g_input_status implemented.
> >>>>
> >>>> Take a look at another SDI driver: drivers/media/spi/gs1662.c
> >>>>
> >>>
> >>> I had a look at the gs1662 driver for the dv_timings callbacks. The gs1662
> >> driver
> >>> requires the timings because it is a SDI Transmitter.
> >>>
> >>> Here the timings are not required as the IP block generates a AXI4 Stream.
> >>> I think it may be required only in case of native / parallel video being
> >> outputted
> >>> as the output stream needs timing information to be decoded.
> >>>
> >>> Please feel free to correct my understanding if wrong.
> >>>
> >>> In the current driver, the input stream properties like width, height, frame
> >> rate,
> >>> progressive/interlaced  are determined from the ST352 packet payload or
> >> from the
> >>> properties detected by the core.
> >>>
> >>> See the xsdirx_get_stream_properties() for details.
> >>
> >> You're wrong. In xsdirx_get_stream_properties() you set the format
> >> information.
> >> But you can't just change that: if the video resolution changes, then that
> means
> >> that userspace needs to be informed that it has changed at the source, it has
> to
> >> find and set the new timings, update the formats, possibly reallocate
> memory
> >> for
> >> the buffers, update other parts of the video pipeline with the new resolution
> >> etc.
> >>
> >> The one thing you cannot do is just pass on the new resolution and hope
> that
> >> the
> >> video pipeline can handle it all.
> >>
> >> The right sequence of events is:
> >>
> >> 1) When a change is detected at the source the driver sends the
> >> SOURCE_CHANGE
> >> event and either stops transmitting to the video pipeline or keeps sending
> the
> >> old resolution (some devices have a freewheeling mode where they can do
> >> that).
> >>
> >> 2) Userspace sees the event, calls QUERY_DV_TIMINGS to find a new timings
> (if
> >> any), usually stops streaming, and calls S_DV_TIMINGS to set the detected
> >> timings:
> >> at that point the driver can configure the output towards the video pipeline
> >> with
> >> the new timings. Userspace reallocates buffers and resumes streaming with
> the
> >> new
> >> resolution.
> >>
> >
> > Thanks for the explanation!
> >
> > I will remove the extraneous video unlock event and stop the streaming when
> video lock / unlock interrupt occurs.
> > I will also implement the g_input_status() to return V4L2_IN_ST_NO_SYNC |
> V4L2_IN_ST_NO_SIGNAL in case video is unlocked.
> >
> > My assumption is that on SOURCE_CHANGE event, application can stop the
> pipeline and then
> > call the G_FORMAT and G_FRAME_INTERVAL to get new frame size, type
> (progressive / interlaced) and frame rate.
> > Is this assumption correct?
> 
> No :-)
> 

Good to have that cleared. :-D

> After SOURCE_CHANGE is received an application calls QUERY_DV_TIMINGS. If
> that
> returns valid timings, then the application calls S_DV_TIMINGS with the
> detected timings. The driver will now update the format, frame interval, etc.
> according to the new timings. And the application can use that to reconfigure
> the video pipeline.
> 
> >
> > Is it mandatory to implement QUERY_DV_TIMINGS with SOURCE_CHANGE
> event?
> 
> Yes.
> 

Thanks again for clarifying this. 

> >
> > I also don't see any V4L2 framework supported events for overflow and
> underflow.
> > Is it ok to keep these or should they be removed too?
> 
> under/overflow of what? Internal fifos? You can keep the custom events for
> that.
>

Yep these are custom events for internal fifos. I will keep them.

Regards
Vishal Sagar

> Regards,
> 
> 	Hans
> 
> >
> > Regards
> >
> > Vishal Sagar
> >
> >> Note that G_DV_TIMINGS returns the last configured timings, not the
> detected
> >> timings: only QUERY_DV_TIMINGS does that.
> >>
> >> In other words: userspace has to retain control of the full pipeline.
> >>
> >> Regards,
> >>
> >> 	Hans
> >>
> >>>
> >>>> Some of the controls you add in this driver can likely be dropped.
> Especially
> >>>> those controls that are not specific to the Xilinx implementation but are
> >>>> generic for any SDI receiver, should be looked at closely: those are
> >>>> candidates for becoming standard controls.
> >>>
> >>> I don't know how other SDI Receiver devices function.
> >>> So I am assuming all these controls are Xilinx specific implementations.
> >>>
> >>>>
> >>>> But the documentation above is simply insufficient for me to tell what is
> >>>> SDI specific and what is implementation specific.
> >>>>
> >>>
> >>> I will add more documentation for these controls.
> >>>
> >>>> Also, I'm no SDI expert, certainly not for the UHD-SDI.
> >>>>
> >>>> Regards,
> >>>>
> >>>>         Hans
> >>>
> >>> Regards
> >>> Vishal Sagar
> >>>
> >

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