linux-kernel - Re: [PATCH v2 1/3] dt-bindings: mediatek: Add a binding for Mediatek JPEG Decoder

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Date:   Thu, 03 Nov 2016 20:33:12 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Rick Chang <rick.chang@...iatek.com>
Cc:     Hans Verkuil <hans.verkuil@...co.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        srv_heupstream@...iatek.com, linux-mediatek@...ts.infradead.org,
        Minghsiu Tsai <minghsiu.tsai@...iatek.com>
Subject: Re: [PATCH v2 1/3] dt-bindings: mediatek: Add a binding for Mediatek JPEG Decoder

Hi Rick,

Thank you for the patch.

On Monday 31 Oct 2016 15:16:55 Rick Chang wrote:
> Add a DT binding documentation for Mediatek JPEG Decoder of
> MT2701 SoC.
> 
> Signed-off-by: Rick Chang <rick.chang@...iatek.com>
> Signed-off-by: Minghsiu Tsai <minghsiu.tsai@...iatek.com>
> ---
>  .../bindings/media/mediatek-jpeg-codec.txt         | 35 +++++++++++++++++++
>  1 file changed, 35 insertions(+)
>  create mode 100644
> Documentation/devicetree/bindings/media/mediatek-jpeg-codec.txt
> 
> diff --git a/Documentation/devicetree/bindings/media/mediatek-jpeg-codec.txt
> b/Documentation/devicetree/bindings/media/mediatek-jpeg-codec.txt new file
> mode 100644
> index 0000000..514e656
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/mediatek-jpeg-codec.txt
> @@ -0,0 +1,35 @@
> +* Mediatek JPEG Codec

Is it a codec or a decoder only ?

> +Mediatek JPEG Codec device driver is a v4l2 driver which can decode
> +JPEG-encoded video frames.

DT bindings should not reference drivers, they are OS-agnostic.

> +Required properties:
> +  - compatible : "mediatek,mt2701-jpgdec"
> +  - reg : Physical base address of the jpeg codec registers and length of
> +        memory mapped region.
> +  - interrupts : interrupt number to the cpu.

That's actually not correct, the interrupt number is local to the interrupt 
controller, not to the CPU.

> +  - clocks : clock name from clock manager

The clocks property doesn't contain a name.

Until we provide standardized descriptions for those properties, I recommend 
copying the compatible, reg, interrupts, clocks, clock-names, power-domains 
and iommus properties descriptions from good DT bindings. Which DT bindings 
are good source of inspiration here is left as an exercise for the reader I'm 
afraid :-(

> +  - clock-names: the clocks of the jpeg codec H/W
> +  - power-domains : a phandle to the power domain.
> +  - larb : must contain the larbes of current platform

Shouldn't this be mediatek,larb ? And what is a larb ?

> +  - iommus : Mediatek IOMMU H/W has designed the fixed associations with
> +        the multimedia H/W. and there is only one multimedia iommu domain.
> +        "iommus = <&iommu portid>" the "portid" is from
> +        dt-bindings\iommu\mt2701-iommu-port.h, it means that this portid
> will
> +        enable iommu. The portid default is disable iommu if "<&iommu> 
portid>"
> +        don't be added.

There are two iommus instances in your example below, this should be 
documented. This description is not very clear I'm afraid.

> +
> +Example:
> +	jpegdec: jpegdec@...04000 {
> +		compatible = "mediatek,mt2701-jpgdec";
> +		reg = <0 0x15004000 0 0x1000>;
> +		interrupts = <GIC_SPI 143 IRQ_TYPE_LEVEL_LOW>;
> +		clocks =  <&imgsys CLK_IMG_JPGDEC_SMI>,
> +			  <&imgsys CLK_IMG_JPGDEC>;
> +		clock-names = "jpgdec-smi",
> +			      "jpgdec";
> +		power-domains = <&scpsys MT2701_POWER_DOMAIN_ISP>;
> +		mediatek,larb = <&larb2>;
> +		iommus = <&iommu MT2701_M4U_PORT_JPGDEC_WDMA>,
> +			 <&iommu MT2701_M4U_PORT_JPGDEC_BSDMA>;
> +	};

-- 
Regards,

Laurent Pinchart