Re: [PATCH v11 1/2] dt-bindings: media: Add Allwinner V3s Camera Sensor Interface (CSI)

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Laurent,

On Fri, Sep 28, 2018 at 12:45:12PM +0300, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Friday, 28 September 2018 12:38:33 EEST Sakari Ailus wrote:
> > On Wed, Sep 26, 2018 at 04:40:04PM +0800, Yong Deng wrote:
> > > Add binding documentation for Allwinner V3s CSI.
> > > 
> > > Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
> > > Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > 
> > I know... but I have a few more comments.
> > 
> > > Reviewed-by: Rob Herring <robh@kernel.org>
> > > Signed-off-by: Yong Deng <yong.deng@magewell.com>
> > > ---
> > > 
> > >  .../devicetree/bindings/media/sun6i-csi.txt        | 59 +++++++++++++++++
> > >  1 file changed, 59 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/media/sun6i-csi.txt
> > > 
> > > diff --git a/Documentation/devicetree/bindings/media/sun6i-csi.txt
> > > b/Documentation/devicetree/bindings/media/sun6i-csi.txt new file mode
> > > 100644
> > > index 000000000000..2ff47a9507a6
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/media/sun6i-csi.txt
> > > @@ -0,0 +1,59 @@
> > > +Allwinner V3s Camera Sensor Interface
> > > +-------------------------------------
> > > +
> > > +Allwinner V3s SoC features two CSI module. CSI0 is used for MIPI CSI-2
> > > +interface and CSI1 is used for parallel interface.
> > > +
> > > +Required properties:
> > > +  - compatible: value must be "allwinner,sun8i-v3s-csi"
> > > +  - reg: base address and size of the memory-mapped region.
> > > +  - interrupts: interrupt associated to this IP
> > > +  - clocks: phandles to the clocks feeding the CSI
> > > +    * bus: the CSI interface clock
> > > +    * mod: the CSI module clock
> > > +    * ram: the CSI DRAM clock
> > > +  - clock-names: the clock names mentioned above
> > > +  - resets: phandles to the reset line driving the CSI
> > > +
> > > +Each CSI node should contain one 'port' child node with one child
> > > 'endpoint' +node, according to the bindings defined in
> > > +Documentation/devicetree/bindings/media/video-interfaces.txt. As
> > > mentioned
> > > +above, the endpoint's bus type should be MIPI CSI-2 for CSI0 and parallel
> > > or +Bt656 for CSI1.
> > 
> > Which port represents CSI0 and which one is CSI1? That needs to be
> > documented.
> 
> There are two CSI devices, named CSI0 and CSI1, with one port each. The CSI0 
> device supports CSI-2 only, and the CSI1 device parallel (BT.601 or BT.656) 
> only.
> 
> > > +
> > > +Endpoint node properties for CSI1
> > 
> > How about CSI0? I'd expect at least data-lanes, and clock-lanes as well if
> > the hardware supports lane mapping.
> 
> I enquired about that too. As far as I understand, CSI0 isn't supported yet in 
> the driver due to lack of documentation and lack of open-source vendor-
> provided source code. While DT bindings are not tied to driver 
> implementations, it's not the best idea to design DT bindings without at least 
> one working implementation to test them. I thus proposed just listing CSI0 as 
> being unsupported for now.

Ack.

We should still define which receiver corresponds to a given port. Probably
1 for CSI1 would make sense, in order to avoid changing the order the
hardware already uses. 0 doesn't need to be documented no IMO.

What do you think?

> 
> > > +---------------------------------
> > > +
> > > +- remote-endpoint	: (required) a phandle to the bus receiver's endpoint
> > > +			   node
> > > +- bus-width:		: (required) must be 8, 10, 12 or 16
> > > +- pclk-sample		: (optional) (default: sample on falling edge)
> > 
> > Could you add that video-interfaces.txt contains documentation of these
> > properties as well? There's a reference above but only discusses port and
> > endpoint nodes.
> > 
> > > +- hsync-active		: (only required for parallel)
> > > +- vsync-active		: (only required for parallel)
> > 
> > As you support both Bt656 and parallel (with sync signals), you can detect
> > the interface type from the presence of these properties. I think you
> > should also say that these properties are not allowed on Bt656. So I'd
> > change this to e.g.
> > 
> > 	(required; parallel-only)
> > 
> > > +
> > > +Example:
> > > +
> > > +csi1: csi@1cb4000 {
> > > +	compatible = "allwinner,sun8i-v3s-csi";
> > > +	reg = <0x01cb4000 0x1000>;
> > > +	interrupts = <GIC_SPI 84 IRQ_TYPE_LEVEL_HIGH>;
> > > +	clocks = <&ccu CLK_BUS_CSI>,
> > > +		 <&ccu CLK_CSI1_SCLK>,
> > > +		 <&ccu CLK_DRAM_CSI>;
> > > +	clock-names = "bus", "mod", "ram";
> > > +	resets = <&ccu RST_BUS_CSI>;
> > > +
> > > +	port {
> > > +		/* Parallel bus endpoint */
> > > +		csi1_ep: endpoint {
> > > +			remote-endpoint = <&adv7611_ep>;
> > > +			bus-width = <16>;
> > > +
> > > +			/* If hsync-active/vsync-active are missing,
> > > +			   embedded BT.656 sync is used */
> > > +			hsync-active = <0>; /* Active low */
> > > +			vsync-active = <0>; /* Active low */
> > > +			pclk-sample = <1>;  /* Rising */
> > > +		};
> > > +	};
> > > +};

-- 
Terveisin,

Sakari Ailus
sakari.ailus@linux.intel.com