Re: [PATCH v3 4/4] [media] dt-bindings: add TI VPIF documentation

[Kevin Hilman <khilman-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>]

Sakari Ailus <sakari.ailus-X3B1VOXEql0@public.gmane.org> writes:

> Hi Rob and Kevin,
>
> On Tue, Nov 29, 2016 at 08:41:44AM -0600, Rob Herring wrote:
>> On Mon, Nov 28, 2016 at 4:30 PM, Kevin Hilman <khilman-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> wrote:
>> > Hi Rob,
>> >
>> > Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> writes:
>> >
>> >> On Tue, Nov 22, 2016 at 07:52:44AM -0800, Kevin Hilman wrote:
>> >>> Signed-off-by: Kevin Hilman <khilman-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>
>> >>> ---
>> >>>  .../bindings/media/ti,da850-vpif-capture.txt       | 65 ++++++++++++++++++++++
>> >>>  .../devicetree/bindings/media/ti,da850-vpif.txt    |  8 +++
>> >>>  2 files changed, 73 insertions(+)
>> >>>  create mode 100644 Documentation/devicetree/bindings/media/ti,da850-vpif-capture.txt
>> >>>  create mode 100644 Documentation/devicetree/bindings/media/ti,da850-vpif.txt
>> >>>
>> >>> diff --git a/Documentation/devicetree/bindings/media/ti,da850-vpif-capture.txt b/Documentation/devicetree/bindings/media/ti,da850-vpif-capture.txt
>> >>> new file mode 100644
>> >>> index 000000000000..c447ac482c1d
>> >>> --- /dev/null
>> >>> +++ b/Documentation/devicetree/bindings/media/ti,da850-vpif-capture.txt
>> >>> @@ -0,0 +1,65 @@
>> >>> +Texas Instruments VPIF Capture
>> >>> +------------------------------
>> >>> +
>> >>> +The TI Video Port InterFace (VPIF) capture component is the primary
>> >>> +component for video capture on the DA850 family of TI DaVinci SoCs.
>> >>> +
>> >>> +TI Document number reference: SPRUH82C
>> >>> +
>> >>> +Required properties:
>> >>> +- compatible: must be "ti,da850-vpif-capture"
>> >>> +- reg: physical base address and length of the registers set for the device;
>> >>> +- interrupts: should contain IRQ line for the VPIF
>> >>> +
>> >>> +VPIF capture has a 16-bit parallel bus input, supporting 2 8-bit
>> >>> +channels or a single 16-bit channel.  It should contain at least one
>> >>> +port child node with child 'endpoint' node. Please refer to the
>> >>> +bindings defined in
>> >>> +Documentation/devicetree/bindings/media/video-interfaces.txt.
>> >>> +
>> >>> +Example using 2 8-bit input channels, one of which is connected to an
>> >>> +I2C-connected TVP5147 decoder:
>> >>> +
>> >>> +    vpif_capture: video-capture@0x00217000 {
>> >>> +            reg = <0x00217000 0x1000>;
>> >>> +            interrupts = <92>;
>> >>> +
>> >>> +            port {
>> >>> +                    vpif_ch0: endpoint@0 {
>> >>> +                              reg = <0>;
>> >>> +                              bus-width = <8>;
>> >>> +                              remote-endpoint = <&composite>;
>> >>> +                    };
>> >>> +
>> >>> +                    vpif_ch1: endpoint@1 {
>> >>
>> >> I think probably channels here should be ports rather than endpoints.
>> >> AIUI, having multiple endpoints is for cases like a mux or 1 to many
>> >> connections. There's only one data flow, but multiple sources or sinks.
>> >
>> > Looking at this closer... , I used an endpoint because it's bascially a
>> > 16-bit parallel bus, that can be configured as (up to) 2 8-bit
>> > "channels.  So, based on the video-interfaces.txt doc, I configured this
>> > as a single port, with (up to) 2 endpoints.  That also allows me to
>> > connect output of the decoder directly, using the remote-endpoint
>> > property.
>> >
>> > So I guess I'm not fully understanding your suggestion.
>> 
>> NM, looks like video-interfaces.txt actually spells out this case and
>> defines doing it as you did.
>
> It's actually the first time I read that portion (at least so that I could
> remember) of video-interfaces.txt. I'm not sure if anyone has implemented
> that previously, nor how we ended up with the text. The list archive could
> probably tell. Cc Guennadi who wrote it. :-) I couldn't immediately find DT
> source with this arrangement.
>
> In case of splitting the port into two parallel interfaces, how do you
> determine which wires belong to which endpoint? I guess they'd be particular
> sets of wires but as there's just a single port it isn't defined by the
> port.

Isn't that the point of data-shift?

e.g. it's a single 16-bit parallel bus, where the lower 8 bits are for
channel 0 and the upper 8 bits are for channel 1.  Alternately, the port
can also be configured as a single 16-bit channel (e.g. for raw
capture.)

If you want more details on this hardware, it's pretty well described in
Chapter 35 of http://www.ti.com/lit/ug/spruh82c/spruh82c.pdf.

FWIW, I'm not really picky about how to do this.  I'm trying to learn
"the right way" and am happy to do that, but the feedback so far has
been confusing (at least for someone relatively new to the DT side of
the media framework.)

Kevin

--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html