Hi Sylwester,
On Thursday 24 January 2013 19:30:10 Sylwester Nawrocki wrote:
> On 01/24/2013 11:16 AM, Laurent Pinchart wrote:
> [...]
>
> >> +Data interfaces on all video devices are described by their child 'port'
> >> +nodes. Configuration of a port depends on other devices participating in
> >> +the data transfer and is described by 'endpoint' subnodes.
> >> +
> >> +dev {
> >> + #address-cells = <1>;
> >> + #size-cells = <0>;
> >> + port@0 {
> >> + endpoint@0 { ... };
> >> + endpoint@1 { ... };
> >> + };
> >> + port@1 { ... };
> >> +};
> >> +
> >> +If a port can be configured to work with more than one other device on
> >> +the same bus, an 'endpoint' child node must be provided for each of
> >> +them. If more than one port is present in a device node or there is more
> >> +than one endpoint at a port, a common scheme, using '#address-cells',
> >> +'#size-cells' and 'reg' properties is used.
> >
> > Wouldn't this cause problems if the device has both video ports and a
> > child bus ? Using #address-cells and #size-cells for the video ports would
> > prevent the child bus from being handled in the usual way.
>
> Indeed, it looks like a serious issue in these bindings.
>
> > A possible solution would be to number ports with a dash instead of a @,
> > as done in pinctrl for instance. We would then get
> >
> > port-0 {
> > endpoint-0 { ... };
> > endpoint-1 { ... };
> > };
> > port-1 { ... };
>
> Sounds like a good alternative, I can't think of any better solution at the
> moment.
>
> >> +Two 'endpoint' nodes are linked with each other through their
> >> +'remote-endpoint' phandles. An endpoint subnode of a device contains
> >> +all properties needed for configuration of this device for data exchange
> >> +with the other device. In most cases properties at the peer 'endpoint'
> >> +nodes will be identical, however they might need to be different when
> >> +there is any signal modifications on the bus between two devices, e.g.
> >> +there are logic signal inverters on the lines.
> >> +
> >> +Required properties
> >> +-------------------
> >> +
> >> +If there is more than one 'port' or more than one 'endpoint' node
> >> following +properties are required in relevant parent node:
> >> +
> >> +- #address-cells : number of cells required to define port number,
> >> should be 1.
> >> +- #size-cells : should be zero.
> >
> > I wonder if we should specify whether a port is a data sink or data
> > source. A source can be connected to multiple sinks at the same time, but
> > a sink can only be connected to a single source. If we want to perform
> > automatic sanity checks in the core knowing the direction might help.
>
> Multiple sources can be linked to a single sink, but only one link can be
> active at any time.
>
> So I'm not sure if knowing if a DT port is a data source or data sink would
> let us to validate device tree structure statically in general.
>
> Such source/sink property could be useful later at runtime, when data
> pipeline is set up for streaming.
Yes, I was mostly thinking about runtime.
> How do you think this could be represented ? By just having boolean
> properties like: 'source' and 'sink' in the port nodes ? Or perhaps in the
> endpoint nodes, since some devices might be bidirectional ? I don't recall
> any at the moment though.
Source and sink properties would do. We could also use a direction property
that could take sink, source and bidirectional values, but that might be more
complex.
I don't think we will have bidirectional link (as that would most probably
involve a very different kind of bus, and thus new bindings).
> >> +Optional endpoint properties
> >> +----------------------------
> >> +
> >> +- remote-endpoint: phandle to an 'endpoint' subnode of the other device
> >> + node.
> >> +- slave-mode: a boolean property, run the link in slave mode.
> >> + Default is master mode.
> >
> > What are master and slave modes ? It might be worth it describing them.
>
> This was originally proposed by Guennadi, I think he knows exactly what's
> the meaning of this property. I'll dig into relevant documentation to
> find out and provide more detailed description.
Thank you.
> >> +- bus-width: number of data lines, valid for parallel busses.
> >> +- data-shift: on parallel data busses, if bus-width is used to specify
> >> + the number of data lines, data-shift can be used to specify which data
> >> + lines are used, e.g. "bus-width=<10>; data-shift=<2>;" means, that
> >> + lines 9:2 are used.
> >> +- hsync-active: active state of HSYNC signal, 0/1 for LOW/HIGH
> >> + respectively.
> >> +- vsync-active: active state of VSYNC signal, 0/1 for LOW/HIGH
> >> + respectively. Note, that if HSYNC and VSYNC polarities are not
> >> + specified, embedded synchronization may be required, where supported.
> >> +- data-active: similar to HSYNC and VSYNC, specifies data line polarity.
> >> +- field-even-active: field signal level during the even field data
> >> + transmission.
> >> +- pclk-sample: sample data on rising (1) or falling (0) edge of the
> >> + pixel clock signal.
> >> +- data-lanes: an array of physical data lane indexes. Position of an
> >> + entry determines the logical lane number, while the value of an entry
> >> + indicates physical lane, e.g. for 2-lane MIPI CSI-2 bus we could have
> >> + "data-lanes = <1>, <2>;", assuming the clock lane is on hardware lane
> >> + 0. This property is valid for serial busses only (e.g. MIPI CSI-2).
> >> +- clock-lanes: an array of physical clock lane indexes. Position of an
> >> + entry determines the logical lane number, while the value of an entry
> >> + indicates physical lane, e.g. for a MIPI CSI-2 bus we could have
> >> + "clock-lanes = <0>;", which places the clock lane on hardware lane 0.
> >> + This property is valid for serial busses only (e.g. MIPI CSI-2). Note
> >> + that for the MIPI CSI-2 bus this array contains only one entry.
> >> +- clock-noncontinuous: a boolean property to allow MIPI CSI-2
> >> + non-continuous clock mode.
> >> +
> >> +Example
> >> +-------
> >> +
> >> +The example snippet below describes two data pipelines. ov772x and
> >> +imx074 are camera sensors with a parallel and serial (MIPI CSI-2) video
> >> +bus respectively. Both sensors are on the I2C control bus corresponding
> >> +to the i2c0 controller node. ov772x sensor is linked directly to the
> >> +ceu0 video host interface. imx074 is linked to ceu0 through the MIPI
> >> +CSI-2 receiver (csi2). ceu0 has a (single) DMA engine writing captured
> >> +data to memory. ceu0 node has a single 'port' node which indicates that
> >> +at any time only one of the following data pipelines can be active:
> >> +ov772x -> ceu0 or imx074 -> csi2 -> ceu0.
> >> +
> >> + ceu0: ceu@0xfe910000 {
> >> + compatible = "renesas,sh-mobile-ceu";
> >> + reg = <0xfe910000 0xa0>;
> >> + interrupts = <0x880>;
> >> +
> >> + mclk: master_clock {
> >> + compatible = "renesas,ceu-clock";
> >> + #clock-cells = <1>;
> >> + clock-frequency = <50000000>; /* Max clock frequency */
> >> + clock-output-names = "mclk";
> >> + };
> >> +
> >> + port {
> >> + #address-cells = <1>;
> >> + #size-cells = <0>;
> >> +
> >> + ceu0_1: endpoint@1 {
> >> + reg = <1>; /* Local endpoint # */
> >> + remote = <&ov772x_1_1>; /* Remote phandle */
> >> + bus-width = <8>; /* Used data lines */
> >> + data-shift = <0>; /* Lines 7:0 are used */
> >
> > As data-shift is optional, shouldn't it be left out when equal to 0 ? It
> > would, however, be nice to have a non-zero data-shift somewhere in the
> > example.
>
> Yes, good point. data-shift could be ommited. I'm going to increase the
> bus-width and make data-shit non-zero.
>
> >> +
> >> + /* If hsync-active/vsync-active are missing,
> >> + embedded bt.605 sync is used */
> >> + hsync-active = <1>; /* Active high */
> >> + vsync-active = <1>; /* Active high */
> >> + data-active = <1>; /* Active high */
> >> + pclk-sample = <1>; /* Rising */
> >> + };
> >> +
> >> + ceu0_0: endpoint@0 {
> >> + reg = <0>;
> >> + remote = <&csi2_2>;
> >> + immutable;
> >
> > What is the immutable property for her e?
>
> I was staring at this yesterday and finally I forgot to remove it. It is
> undocumented and I think it's not supposed to be here. Guennadi, would
> you have any comments on that ?
>
> >> + };
> >> + };
> >> + };
> >> +
> >> + i2c0: i2c@0xfff20000 {
> >> + ...
> >> + ov772x_1: camera@0x21 {
> >> + compatible = "omnivision,ov772x";
> >> + reg = <0x21>;
> >> + vddio-supply = <®ulator1>;
> >> + vddcore-supply = <®ulator2>;
> >> +
> >> + clock-frequency = <20000000>;
> >> + clocks = <&mclk 0>;
> >> + clock-names = "xclk";
> >> +
> >> + port {
> >> + /* With 1 endpoint per port no need in addresses. */
> >
> > s/in/for/ ?
>
> I proposed same change to Guennadi, but he argued that "in" is also
> commonly used. I agreed even though 'for' seemed more natural to me.
> I would change it, unless there is a strong opposition. :)
--
Regards,
Laurent Pinchart
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