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

Laurent Pinchart
2016-11-03T18:34:50Z

Hi Rick,

A few more comments.

On Thursday 03 Nov 2016 20:33:12 Laurent Pinchart wrote:
> 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@mediatek.com>
> > Signed-off-by: Minghsiu Tsai <minghsiu.tsai@mediatek.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"

Is the JPEG decoder found in MT2701 only, or in other Mediatek SoCs as well ?

> > + - 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.

Furthermore you should document which clocks need to be specified here. There
are two of them in the example below, the documentation should explain this
clearly.

> 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@15004000 {
> > + 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