linux-kernel - Re: [PATCH 1/4] Documentation: dt: Add bindings documentation for DW MIPI CSI-2 Host

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Date:   Wed, 15 Mar 2017 13:26:44 -0500
From:   Rob Herring <robh@...nel.org>
To:     Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>
Cc:     linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, CARLOS.PALMINHA@...opsys.com,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, Benoit Parrot <bparrot@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Hugues Fruchet <hugues.fruchet@...com>,
        Jean-Christophe Trotin <jean-christophe.trotin@...com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Mark Rutland <mark.rutland@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Minghsiu Tsai <minghsiu.tsai@...iatek.com>,
        Peter Griffin <peter.griffin@...aro.org>,
        Rick Chang <rick.chang@...iatek.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Simon Horman <simon.horman@...ronome.com>,
        Songjun Wu <songjun.wu@...rochip.com>,
        Tiffany Lin <tiffany.lin@...iatek.com>
Subject: Re: [PATCH 1/4] Documentation: dt: Add bindings documentation for DW
 MIPI CSI-2 Host

On Tue, Mar 07, 2017 at 02:37:48PM +0000, Ramiro Oliveira wrote:
> Create device tree bindings documentation for the Synopsys DW MIPI CSI-2
>  Host.
> 
> Signed-off-by: Ramiro Oliveira <roliveir@...opsys.com>
> ---
>  .../devicetree/bindings/media/snps,dw-mipi-csi.txt | 37 ++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/media/snps,dw-mipi-csi.txt
> 
> diff --git a/Documentation/devicetree/bindings/media/snps,dw-mipi-csi.txt b/Documentation/devicetree/bindings/media/snps,dw-mipi-csi.txt
> new file mode 100644
> index 000000000000..5b24eb43d760
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/snps,dw-mipi-csi.txt
> @@ -0,0 +1,37 @@
> +Synopsys DesignWare CSI-2 Host controller
> +
> +Description
> +-----------
> +
> +This HW block is used to receive image coming from an MIPI CSI-2 compatible
> +camera.
> +
> +Required properties:
> +- compatible: shall be "snps,dw-mipi-csi"

... "and an SoC specific compatible string"

> +- reg		: physical base address and size of the device memory mapped
> +  registers;
> +- interrupts	: CSI-2 Host interrupt
> +- output-type   : Core output to be used (IPI-> 0 or IDI->1 or BOTH->2) These
> +  values choose which of the Core outputs will be used, it can be Image Data
> +  Interface or Image Pixel Interface.
> +- phys: List of one PHY specifier (as defined in
> +  Documentation/devicetree/bindings/phy/phy-bindings.txt). This PHY is a MIPI
> +  DPHY working in RX mode.
> +- resets: Reference to a reset controller (optional)
> +
> +Optional properties(if in IPI mode):
> +- ipi-mode 	: Mode to be used when in IPI(Camera -> 0 or Controller -> 1)
> +  This property defines if the controller will use the video timings available
> +  in the video stream or if it will use pre-defined ones.

This could be boolean instead. I'd expect the former to be the typical 
mode, so name the property for the latter.

> +- ipi-color-mode: Bus depth to be used in IPI (48 bits -> 0 or 16 bits -> 1)
> +  This property defines the width of the IPI bus.

Are these the only 2 modes that any h/w would ever have (not just your 
controller)? Perhaps using the actual bits for the value would be 
better. Also, if this is the bus width, then the property should be 
named that as bus widths and pixel formats or color modes are not 
necessarily the same.

> +- ipi-auto-flush: Data auto-flush (1 -> Yes or 0 -> No). This property defines
> +  if the data is automatically flushed in each vsync or if this process is done
> +  manually

This could be boolean.

> +- virtual-channel: Virtual channel where data is present when in IPI mode. This
> +  property chooses the virtual channel which IPI will use to retrieve the video
> +  stream.

Again, some of these should probably be common properties (and therefore 
documented in a common location). I'm looking for some feedback from 
video/camera maintainers on this. I know I've seen some other similar 
bindings for camera interfaces recently.

Rob