Re: [V9, 1/2] media: dt-bindings: media: i2c: Document OV02A10 bindings

From: Dongchun Zhu <dongchun.zhu@mediatek.com>
To: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	"Rob Herring" <robh@kernel.org>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	srv_heupstream <srv_heupstream@mediatek.com>,
	devicetree@vger.kernel.org,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Shengnan Wang (王圣男)" <shengnan.wang@mediatek.com>,
	"Tomasz Figa" <tfiga@chromium.org>,
	"Bartosz Golaszewski" <bgolaszewski@baylibre.com>,
	"Sj Huang" <sj.huang@mediatek.com>,
	"Nicolas Boichat" <drinkcat@chromium.org>,
	"moderated list:ARM/Mediatek SoC support"
	<linux-mediatek@lists.infradead.org>,
	dongchun.zhu@mediatek.com, "Louis Kuo" <louis.kuo@mediatek.com>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Cao Bing Bu" <bingbu.cao@intel.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	"Linux Media Mailing List" <linux-media@vger.kernel.org>
Subject: Re: [V9, 1/2] media: dt-bindings: media: i2c: Document OV02A10 bindings
Date: Thu, 28 May 2020 11:34:42 +0800	[thread overview]
Message-ID: <1590636882.8804.474.camel@mhfsdcap03> (raw)
In-Reply-To: <20200527211628.GT7618@paasikivi.fi.intel.com>

Hi Sakari, Rob,

On Thu, 2020-05-28 at 00:16 +0300, Sakari Ailus wrote:
> Hi Rob, Dongchun,
> 
> On Wed, May 27, 2020 at 09:27:22AM -0600, Rob Herring wrote:
> > > > > +    properties:
> > > > > +      endpoint:
> > > > > +        type: object
> > > > > +        additionalProperties: false
> > > > > +
> > > > > +        properties:
> > >
> > > Actually I wonder whether we need to declare 'clock-lanes' here?
> > 
> > Yes, if you are using it.
> 
> Dongchun, can you confirm the chip has a single data and a single clock
> lane and that it does not support lane reordering?
> 

From the datasheet, 'MIPI inside the OV02A10 provides one single
uni-directional clock lane and one bi-directional data lane solution for
communication links between components inside a mobile device.
The data lane has full support for HS(uni-directional) and
LP(bi-directional) data transfer mode.'

The sensor doesn't support lane reordering, so 'clock-lanes' property
would not be added in next release.

> So if there's nothing to convey to the driver, also the data-lanes should
> be removed IMO.
> 

However, 'data-lanes' property may still be required.
It is known that either data-lanes or clock-lanes is an array of
physical data lane indexes. Position of an entry determines the logical
lane number, while the value of an entry indicates physical lane, e.g.,
for 1-lane MIPI CSI-2 bus we could have "data-lanes = <1>;", assuming
the clock lane is on hardware lane 0.

As mentioned earlier, the OV02A10 sensor supports only 1C1D and does not
support lane reordering, so here we shall use 'data-lanes = <1>' as
there is only a clock lane for OV02A10.

Reminder:
If 'data-lanes' property is not present, the driver would assume
four-lane operation. This means for one-lane or two-lane operation, this
property must be present and set to the right physical lane indexes.
If the hardware does not support lane reordering, monotonically
incremented values shall be used from 0 or 1 onwards, depending on
whether or not there is also a clock lane.

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