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Subject: Re: [PATCH v3 01/24] [media] dt-bindings: Add bindings for i.MX media
 driver
To: Philipp Zabel <p.zabel@pengutronix.de>
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From: Steve Longerbeam <slongerbeam@gmail.com>
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Date: Fri, 13 Jan 2017 11:03:22 -0800
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On 01/13/2017 03:55 AM, Philipp Zabel wrote:
> Am Freitag, den 06.01.2017, 18:11 -0800 schrieb Steve Longerbeam:
>> Add bindings documentation for the i.MX media driver.
>>
>> Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
>> ---
>>   Documentation/devicetree/bindings/media/imx.txt | 57 +++++++++++++++++++++++++
>>   1 file changed, 57 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/media/imx.txt
>>
>> diff --git a/Documentation/devicetree/bindings/media/imx.txt b/Documentation/devicetree/bindings/media/imx.txt
>> new file mode 100644
>> index 0000000..254b64a
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/media/imx.txt
>> @@ -0,0 +1,57 @@
>> +Freescale i.MX Media Video Devices
>> +
>> +Video Media Controller node
>> +---------------------------
>> +
>> +This is the parent media controller node for video capture support.
>> +
>> +Required properties:
>> +- compatible : "fsl,imx-media";
> Would you be opposed to calling this "capture-subsystem" instead of
> "imx-media"? We already use "fsl,imx-display-subsystem" and
> "fsl,imx-gpu-subsystem" for the display and GPU compound devices.

sure. Some pie-in-the-sky day when DRM and media are unified,
there could be a single device that handles them all, but for now
I'm fine with "fsl,capture-subsystem".

>> +- ports      : Should contain a list of phandles pointing to camera
>> +  	       sensor interface ports of IPU devices
>> +
>> +
>> +fim child node
>> +--------------
>> +
>> +This is an optional child node of the ipu_csi port nodes. If present and
>> +available, it enables the Frame Interval Monitor. Its properties can be
>> +used to modify the method in which the FIM measures frame intervals.
>> +Refer to Documentation/media/v4l-drivers/imx.rst for more info on the
>> +Frame Interval Monitor.
>> +
>> +Optional properties:
>> +- fsl,input-capture-channel: an input capture channel and channel flags,
>> +			     specified as <chan flags>. The channel number
>> +			     must be 0 or 1. The flags can be
>> +			     IRQ_TYPE_EDGE_RISING, IRQ_TYPE_EDGE_FALLING, or
>> +			     IRQ_TYPE_EDGE_BOTH, and specify which input
>> +			     capture signal edge will trigger the input
>> +			     capture event. If an input capture channel is
>> +			     specified, the FIM will use this method to
>> +			     measure frame intervals instead of via the EOF
>> +			     interrupt. The input capture method is much
>> +			     preferred over EOF as it is not subject to
>> +			     interrupt latency errors. However it requires
>> +			     routing the VSYNC or FIELD output signals of
>> +			     the camera sensor to one of the i.MX input
>> +			     capture pads (SD1_DAT0, SD1_DAT1), which also
>> +			     gives up support for SD1.
> This is a clever method to get better frame timestamps. Too bad about
> the routing requirements. Can this be used on Nitrogen6X?

Absolutely, this support just needs use of the input-capture channels in the
imx GPT. I still need to submit the patch to the imx-gpt driver that adds an
input capture API, so at this point fsl,input-capture-channel has no effect,
but it does work (tested on SabreAuto).

>
>> +
>> +mipi_csi2 node
>> +--------------
>> +
>> +This is the device node for the MIPI CSI-2 Receiver, required for MIPI
>> +CSI-2 sensors.
>> +
>> +Required properties:
>> +- compatible	: "fsl,imx6-mipi-csi2";
> I think this should get an additional "snps,dw-mipi-csi2" compatible,
> since the only i.MX6 specific part is the bolted-on IPU2CSI gasket.

right, minus the gasket it's a Synopsys core. I'll add that compatible flag.
Or should wait until the day this subdev is exported for general use, after
pulling out the gasket specifics?


>
>> +- reg           : physical base address and length of the register set;
>> +- clocks	: the MIPI CSI-2 receiver requires three clocks: hsi_tx
>> +                  (the DPHY clock), video_27m, and eim_sel;
> Note that hsi_tx is incorrectly named. CCGR3[CG8] just happens to be the
> shared gate bit that gates the HSI clocks as well as the MIPI
> "ac_clk_125m", "cfg_clk", "ips_clk", and "pll_refclk" inputs to the mipi
> csi-2 core, but we are missing shared gate clocks in the clock tree for
> these.

Yes, so many clocks for the MIPI core. Why so many? I would think
there would need to be at most three: a clock for the MIPI CSI-2 core
and HSI core, and a clock for the D-PHY (oh and maybe a clock for an
M-PHY if there is one). I have no clue what all these other clocks are.
But anyway, a single gating bit, CCGR3[CG8], seems to enable them all.

> Both cfg_clk and pll_refclk are sourced from video_27m, so "cfg" ->
> video_27m seems fine.
> But I don't get "dphy".

I presume it's the clock for the D-PHY.

>   Which input clock would that correspond to?
> "pll_refclk?"

the mux at CDCDR says it comes from PLL3_120M, or PLL2_PFD2.


> Also the pixel clock input is a gate after aclk_podf (which we call
> eim_podf), not aclk_sel (eim_sel).

ok, I'll switch to eim_podf for the pixel clock.

Steve

>
>> +- clock-names	: must contain "dphy", "cfg", "pix";
>> +
>> +Optional properties:
>> +- interrupts	: must contain two level-triggered interrupts,
>> +                  in order: 100 and 101;
> regards
> Philipp
>