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

From: Sakari Ailus <sakari.ailus@linux.intel.com>
To: Chen-Yu Tsai <wens@csie.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Yong Deng <yong.deng@magewell.com>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	David Miller <davem@davemloft.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Hans Verkuil <hans.verkuil@cisco.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Jacob Chen <jacob-chen@iotwrt.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Thierry Reding <treding@nvidia.com>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Todor Tomov <todor.tomov@linaro.org>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	devicetree <devicetree@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-sunxi <linux-sunxi@googlegroups.com>
Subject: Re: [PATCH v11 1/2] dt-bindings: media: Add Allwinner V3s Camera Sensor Interface (CSI)
Date: Fri, 28 Sep 2018 15:56:01 +0300	[thread overview]
Message-ID: <20180928125601.6ye5tvrmh57amvh5@paasikivi.fi.intel.com> (raw)
In-Reply-To: <CAGb2v65YpPRHb5YiGJhC8NX5F5i3+1rW5y6Dq5L+pNN3U_uLdQ@mail.gmail.com>

Hi Chen-Yu,

On Fri, Sep 28, 2018 at 07:10:58PM +0800, Chen-Yu Tsai wrote:
> On Fri, Sep 28, 2018 at 6:23 PM Sakari Ailus
> <sakari.ailus@linux.intel.com> wrote:
> >
> > 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?
> 
> AFAICT it would be a completely seperate node, since they have different address
> spaces, clocks and reset controls. So there's no possibility of confusion.
> 
> According to Yong, CSI0 is tied internally to some unknown MIPI CSI2-receiver,
> which is the undocumented part. CSI1 has its parallel data pins exposed to the
> outside.

Thanks for clearing up the confusion. If these are truly different kinds of
devices, then don't they also deserve different compatible strings? And
possibly also different DT binding documentation in a separate file.

-- 
Regards,

Sakari Ailus
sakari.ailus@linux.intel.com