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Date:   Wed, 21 Nov 2018 23:56:50 +0200
From:   Sakari Ailus <sakari.ailus@linux.intel.com>
To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     Hans Verkuil <hans.verkuil@cisco.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        linux-media@vger.kernel.org, Andrzej Hajda <a.hajda@samsung.com>,
        Chen-Yu Tsai <wens@csie.org>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>
Subject: Re: [PATCH 1/5] dt-bindings: media: Add Allwinner A10 CSI binding
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Hi Maxime,

On Thu, Nov 15, 2018 at 08:04:24PM +0100, Maxime Ripard wrote:
> Hi Sakari,
> 
> On Tue, Nov 13, 2018 at 10:38:55AM +0200, Sakari Ailus wrote:
> > > +  - allwinner,has-isp: Whether the CSI controller has an ISP
> > > +                       associated to it or not
> > 
> > Is the ISP a part of the same device? It sounds like that this is actually
> > a different device if it contains an ISP as well, and that should be
> > apparent from the compatible string. What do you think?
> 
> I guess we can see it as both. It seems to be the exact same register
> set, except for the fact that the first instance has that ISP in
> addition, and several channels, as you pointed out in your other mail.

I'm simply referring to existing practices as far as I know them. If it's a
different device, it should have a different compatible string, not a
vendor-specific property to tell it's somehow different.

Many SoCs also separate the DMA and the CSI-2 receivers, and thus they have
separate drivers. I don't know about your case, but the ISP requiring a
different clock is a hint.

> 
> What these channels are is not exactly clear. It looks like it's
> related to the BT656 interface where you could interleave channel
> bytes over the bus. I haven't really looked into it, and it doesn't
> look like we have any code (or hardware) able to do that though.
> 
> > > +
> > > +If allwinner,has-isp is set, an additional "isp" clock is needed,
> > > +being a phandle to the clock driving the ISP.
> > > +
> > > +The 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. The
> > > +endpoint's bus type must be parallel or BT656.
> > > +
> > > +Endpoint node properties for CSI
> > > +---------------------------------
> > > +
> > > +- remote-endpoint	: (required) a phandle to the bus receiver's endpoint
> > > +			   node
> > 
> > Rob's opinion has been (AFAIU) that this is not needed as it's already a
> > part of the graph bindings. Unless you want to say that it's required, that
> > is --- the graph bindings document it as optional.
> 
> Ok, I'll remove it.
> 
> > > +- bus-width:		: (required) must be 8
> > 
> > If this is the only value the hardware supports, I don't see why you should
> > specify it here.
> 
> Ditto :)
> 
> > > +- pclk-sample		: (optional) (default: sample on falling edge)
> > > +- hsync-active		: (only required for parallel)
> > > +- vsync-active		: (only required for parallel)
> > > +
> > > +Example:
> > > +
> > > +csi0: csi@1c09000 {
> > > +	compatible = "allwinner,sun7i-a20-csi",
> > > +		     "allwinner,sun4i-a10-csi";
> > > +	reg = <0x01c09000 0x1000>;
> > > +	interrupts = <GIC_SPI 42 IRQ_TYPE_LEVEL_HIGH>;
> > > +	clocks = <&ccu CLK_AHB_CSI0>, <&ccu CLK_CSI0>,
> > > +		 <&ccu CLK_CSI_SCLK>, <&ccu CLK_DRAM_CSI0>;
> > > +	clock-names = "ahb", "mod", "isp", "ram";
> > > +	resets = <&ccu RST_CSI0>;
> > > +	allwinner,csi-channels = <4>;
> > > +	allwinner,has-isp;
> > > +	
> > > +	port {
> > > +		csi_from_ov5640: endpoint {
> > > +                        remote-endpoint = <&ov5640_to_csi>;
> > > +                        bus-width = <8>;
> > > +                        data-shift = <2>;
> > 
> > data-shift needs to be documented above if it's relevant for the device.
> 
> It's not really related to the CSI device in that case but the sensor,
> so I'll just leave it out.

Hmm. data-shift should only be relevant for the receiver, shoudn't it?

-- 
Regards,

Sakari Ailus
sakari.ailus@linux.intel.com