Message-ID: <20170207204617.GD13854@valkosipuli.retiisi.org.uk>
Date:   Tue, 7 Feb 2017 22:46:17 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
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,
        p.zabel@...gutronix.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, Sascha Hauer <s.hauer@...gutronix.de>,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v3 13/24] platform: add video-multiplexer subdevice driver

Hi Steve,

On Fri, Jan 06, 2017 at 06:11:31PM -0800, Steve Longerbeam wrote:
> From: Philipp Zabel <p.zabel@...gutronix.de>
> 
> This driver can handle SoC internal and external video bus multiplexers,
> controlled either by register bit fields or by a GPIO. The subdevice
> passes through frame interval and mbus configuration of the active input
> to the output side.
> 
> Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> 
> --
> 
> - fixed a cut&paste error in vidsw_remove(): v4l2_async_register_subdev()
>   should be unregister.
> 
> - added media_entity_cleanup() and v4l2_device_unregister_subdev()
>   to vidsw_remove().
> 
> - there was a line left over from a previous iteration that negated
>   the new way of determining the pad count just before it which
>   has been removed (num_pads = of_get_child_count(np)).
> 
> - Philipp Zabel has developed a set of patches that allow adding
>   to the subdev async notifier waiting list using a chaining method
>   from the async registered callbacks (v4l2_of_subdev_registered()
>   and the prep patches for that). For now, I've removed the use of
>   v4l2_of_subdev_registered() for the vidmux driver's registered
>   callback. This doesn't affect the functionality of this driver,
>   but allows for it to be merged now, before adding the chaining
>   support.
> 
> Signed-off-by: Steve Longerbeam <steve_longerbeam@...tor.com>
> ---
>  .../bindings/media/video-multiplexer.txt           |  59 +++
>  drivers/media/platform/Kconfig                     |   8 +
>  drivers/media/platform/Makefile                    |   2 +
>  drivers/media/platform/video-multiplexer.c         | 472 +++++++++++++++++++++
>  4 files changed, 541 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/media/video-multiplexer.txt
>  create mode 100644 drivers/media/platform/video-multiplexer.c
> 
> diff --git a/Documentation/devicetree/bindings/media/video-multiplexer.txt b/Documentation/devicetree/bindings/media/video-multiplexer.txt
> new file mode 100644
> index 0000000..9d133d9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/video-multiplexer.txt
> @@ -0,0 +1,59 @@
> +Video Multiplexer
> +=================
> +
> +Video multiplexers allow to select between multiple input ports. Video received
> +on the active input port is passed through to the output port. Muxes described
> +by this binding may be controlled by a syscon register bitfield or by a GPIO.
> +
> +Required properties:
> +- compatible : should be "video-multiplexer"
> +- reg: should be register base of the register containing the control bitfield
> +- bit-mask: bitmask of the control bitfield in the control register
> +- bit-shift: bit offset of the control bitfield in the control register
> +- gpios: alternatively to reg, bit-mask, and bit-shift, a single GPIO phandle
> +  may be given to switch between two inputs
> +- #address-cells: should be <1>
> +- #size-cells: should be <0>
> +- port@*: at least three port nodes containing endpoints connecting to the
> +  source and sink devices according to of_graph bindings. The last port is
> +  the output port, all others are inputs.
> +
> +Example:
> +
> +syscon {
> +	compatible = "syscon", "simple-mfd";
> +
> +	mux {

Could you use standardised properties for this, i.e. ones defined in
Documentation/devicetree/bindings/media/video-interfaces.txt ?

This is very similar to another patch "[PATCH] devicetree: Add video bus
switch" posted by Pavel Machek recently. The problem with that is also
similar than with this one: how to pass the CSI-2 bus configuration to the
receiver.

There's some discussion here:

<URL:http://www.spinics.net/lists/linux-media/msg109493.html>

As Laurent already suggested, I think we should have a common solution for
the problem that, besides conveying the bus parameters to the receiver, also
encompasses CSI-2 virtual channels and data types.

That would mean finishing the series of patches in the branch I believe
Laurent already quoted here.

> +		compatible = "video-multiplexer";
> +		/* Single bit (1 << 19) in syscon register 0x04: */
> +		reg = <0x04>;
> +		bit-mask = <1>;
> +		bit-shift = <19>;
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port@0 {
> +			reg = <0>;
> +
> +			mux_in0: endpoint {
> +				remote-endpoint = <&video_source0_out>;
> +			};
> +		};
> +
> +		port@1 {
> +			reg = <1>;
> +
> +			mux_in1: endpoint {
> +				remote-endpoint = <&video_source1_out>;
> +			};
> +		};
> +
> +		port@2 {
> +			reg = <2>;
> +
> +			mux_out: endpoint {
> +				remote-endpoint = <&capture_interface_in>;
> +			};
> +		};
> +	};
> +};

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@....fi	XMPP: sailus@...iisi.org.uk

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