linux-kernel - Re: [PATCH v3 01/24] [media] dt-bindings: Add bindings for i.MX media driver

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Date:   Fri, 13 Jan 2017 12:55:51 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Steve Longerbeam <slongerbeam@...il.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com,
        linux@...linux.org.uk, mchehab@...nel.org, hverkuil@...all.nl,
        nick@...anahar.org, markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, bparrot@...com,
        geert@...ux-m68k.org, arnd@...db.de, sudipm.mukherjee@...il.com,
        minghsiu.tsai@...iatek.com, tiffany.lin@...iatek.com,
        jean-christophe.trotin@...com, horms+renesas@...ge.net.au,
        niklas.soderlund+renesas@...natech.se, robert.jarzmik@...e.fr,
        songjun.wu@...rochip.com, andrew-ct.chen@...iatek.com,
        gregkh@...uxfoundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v3 01/24] [media] dt-bindings: Add bindings for i.MX
 media driver

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@...tor.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.

> +- 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?

> +
> +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.

> +- 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.
Both cfg_clk and pll_refclk are sourced from video_27m, so "cfg" ->
video_27m seems fine.
But I don't get "dphy". Which input clock would that correspond to?
"pll_refclk?"
Also the pixel clock input is a gate after aclk_podf (which we call
eim_podf), not aclk_sel (eim_sel).

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

regards
Philipp