[PATCH] media: add V4L2 DT binding documentation
Guennadi Liakhovetski
g.liakhovetski at gmx.de
Tue Sep 25 10:59:09 EDT 2012
Hi Sylwester
Ok, looks like there are no more comments coming, so, we can submit a new
version:-)
Thanks for your comments:
On Tue, 11 Sep 2012, Sylwester Nawrocki wrote:
> Hi Guennadi,
>
> On 09/11/2012 05:51 PM, Guennadi Liakhovetski wrote:
> > This patch adds a document, describing common V4L2 device tree bindings.
> >
> > Co-authored-by: Sylwester Nawrocki <s.nawrocki at samsung.com>
> > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski at gmx.de>
> > ---
> > Documentation/devicetree/bindings/media/v4l2.txt | 143 ++++++++++++++++++++++
> > 1 files changed, 143 insertions(+), 0 deletions(-)
> > create mode 100644 Documentation/devicetree/bindings/media/v4l2.txt
> >
> > diff --git a/Documentation/devicetree/bindings/media/v4l2.txt b/Documentation/devicetree/bindings/media/v4l2.txt
> > new file mode 100644
> > index 0000000..55da6de
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/media/v4l2.txt
> > @@ -0,0 +1,143 @@
> > +Video4Linux Version 2 (V4L2)
> > +
> > +General concept:
> > +- video pipelines consist of external devices, e.g., camera sensors, controlled
> > + over an I2C bus, and SoC internal IP blocks, including video DMA engines and
> > + video data processors.
> > +- this document describes common bindings of all video pipeline devices.
> > +- SoC internal blocks are described by DT nodes, placed similarly to other SoC
> > + blocks.
> > +- external devices are places on their respective control busses, e.g., I2C
> > +- data interfaces on all video devices are described by "port" child DT nodes
> > +- port configuration depends on other devices, participating in the data
> > + transfer, and is described by "link" DT nodes, specified as children of
> > + all "port" nodes, connected to this bus.
> > +- if a port can be configured to work with more than one other device on the
> > + same bus, a "link" child DT node must be provided for each of them.
> > +- if more than one port is present on a device or more than one link is
> > + connected to a port, a common scheme, using "#address-cells," "#size-cells"
> > + and "reg" properties is used.
>
> How about rephrasing/rearranging this to:
>
> This document describes common bindings of all video pipeline devices.
>
> General concept
> ---------------
>
> Video pipelines consist of external devices, e.g. camera sensors, controlled
> over an I2C, SPI or UART bus, and SoC internal IP blocks, including video DMA
> engines and video data processors.
> SoC internal blocks are described by DT nodes, placed similarly to other SoC
> blocks. External devices are represented as child nodes of their respective
> bus controller nodes, e.g. I2C.
Well, I don't mind. I looked at a random file under
Documentation/devicetree/bindings and used the same style, but we can use
a free-flowing text too.
> Data interfaces on all video devices are described by "port" child DT nodes.
> Configuration of a port depends on other devices participating in the data
> transfer and is described by "link" DT nodes, specified as children of the
> "port" nodes:
>
> /foo {
> port at 0 {
> link at 0 { ... };
> link at 1 { ... };
> };
> port at 1 { ... };
> };
>
> If a port can be configured to work with more than one other device on the
> same bus, a "link" child DT node must be provided for each of them.
> If more than one port is present on a device or more than one link is
> connected to a port, a common scheme, using "#address-cells" "#size-cells"
> and "reg" properties is used.
>
> > +Optional link properties:
> > +- remote: phandle to the other endpoint link DT node.
> > +- data-shift: on parallel data busses, if data-width is used to specify the
>
> s/busses/buses
Nnnnooo... I think, "busses" is British and "buses" is American English,
and I'm usually trying to follow the former, as much as I can:-) Also see
"drivers/i2c/busses/"
> > + number of data lines, data-shift can be used to specify which data lines are
> > + used, e.g., "data-width=<10>; data-shift=<2>;" means, that lines 9:2 are used.
> > +- hsync-active: 1 or 0 for active-high or -low HSYNC signal polarity
> > + respectively.
> > +- vsync-active: ditto for VSYNC. Note, that if HSYNC and VSYNC polarities are
> > + not specified, embedded synchronisation may be required, where supported.
> > +- pclk-sample: rising (1) or falling (0) edge to sample the pixel clock pin.
> > +- immutable: used for SoC-internal links, if no configuration is required.
> > +- data-lanes: array of serial, e.g., MIPI CSI-2, data hardware lane numbers in
>
> nit: s/e.g.,/e.g. ?
This is a good question, actually. Until now I've been following a
suggestion by some well-educated British friend of mine, who told me to
use commas on either side of "e.g." and "i.e." But in most textx I read I
indeed see only one comma - before those. So, I tried to search and got a
couple of hits, which suggest, that putting a comma on both sides or at
least _after_ those abbreviations is more American grammar, and only
before is more British... So, I think I'll follow your advise on this too
and switch to the no-comma-after style, thanks.
> > + the ascending order, beginning with logical lane 0.
> > +- clock-lanes: hardware lane number, used for the clock lane.
>
> s/clock lane/clock ?
Well, to me both make sense. The meanings are a bit different, but none
seems wrong to me. My version seems a bit more specific - not just "some"
clock, but the CSI-2 clock lane?
> > +
> > +Example:
> > +
> > + ceu0: ceu at 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: link at 1 {
> > + reg = <1>; /* local link # */
> > + remote = <&ov772x_1_1>; /* remote phandle */
> > + bus-width = <8>; /* used data lines */
> > + data-shift = <0>; /* lines 7:0 are used */
> > +
> > + /* If [hv]sync-active are missing, embedded bt.605 sync is used */
> > + hsync-active = <1>; /* active high */
> > + vsync-active = <1>; /* active high */
> > + pclk-sample = <1>; /* rising */
> > + };
> > +
> > + ceu0_0: link at 0 {
> > + reg = <0>;
> > + remote = <&csi2_2>;
> > + immutable;
> > + };
> > + };
> > + };
> > +
> > + i2c0: i2c at 0xfff20000 {
> > + ...
> > + ov772x_1: camera at 0x21 {
> > + compatible = "omnivision,ov772x";
> > + reg = <0x21>;
> > + vddio-supply = <®ulator1>;
> > + vddcore-supply = <®ulator2>;
> > +
> > + clock-frequency = <20000000>;
> > + clocks = <&mclk 0>;
> > + clock-names = "xclk";
> > +
> > + port {
> > + /* With 1 link per port no need in addresses */
>
> s/in/for ?
Ehm, no idea either. Both "no need in" and "no need for" produce enough
hits in search engines:-)
> > + ov772x_1_1: link {
> > + bus-width = <8>;
> > + remote = <&ceu0_1>;
> > + hsync-active = <1>;
> > + hsync-active = <0>; /* who came up with an inverter here?... */
> > + pclk-sample = <1>;
> > + };
> > + };
> > + };
> > +
> > + imx074: camera at 0x1a {
> > + compatible = "sony,imx074";
> > + reg = <0x1a>;
> > + vddio-supply = <®ulator1>;
> > + vddcore-supply = <®ulator2>;
> > +
> > + clock-frequency = <30000000>; /* shared clock with ov772x_1 */
> > + clocks = <&mclk 0>;
> > + clock-names = "sysclk"; /* assuming this is the name in the datasheet */
> > +
> > + port {
> > + imx074_1: link {
> > + clock-lanes = <0>;
> > + data-lanes = <1>, <2>;
> > + remote = <&csi2_1>;
> > + };
> > + };
> > + };
> > + };
> > +
> > + csi2: csi2 at 0xffc90000 {
> > + compatible = "renesas,sh-mobile-csi2";
> > + reg = <0xffc90000 0x1000>;
> > + interrupts = <0x17a0>;
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > +
> > + port at 1 {
> > + compatible = "renesas,csi2c"; /* one of CSI2I and CSI2C */
> > + reg = <1>; /* CSI-2 PHY #1 of 2: PHY_S, PHY_M has port address 0, is unused */
> > +
> > + csi2_1: link {
> > + clock-lanes = <0>;
> > + data-lanes = <2>, <1>;
> > + remote = <&imx074_1>;
> > + };
> > + };
> > + port at 2 {
> > + reg = <2>; /* port 2: link to the CEU */
> > +
> > + csi2_2: link {
> > + immutable;
> > + remote = <&ceu0_0>;
> > + };
> > + };
> > + };
>
> --
>
> Regards,
> Sylwester
>
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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