Re: [PATCH 08/13] dt-bindings: media: ov5640: Remove data-shift

From: Sakari Ailus <sakari.ailus@iki.fi>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Jacopo Mondi <jacopo+renesas@jmondi.org>,
	robh+dt@kernel.org, devicetree@vger.kernel.org,
	slongerbeam@gmail.com, linux-media@vger.kernel.org,
	linux-renesas-soc@vger.kernel.org,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@st.com>,
	"moderated list:ARM/STM32 ARCHITECTURE" 
	<linux-stm32@st-md-mailman.stormreply.com>
Subject: Re: [PATCH 08/13] dt-bindings: media: ov5640: Remove data-shift
Date: Sun, 26 Jul 2020 00:18:33 +0300	[thread overview]
Message-ID: <20200725211833.GE829@valkosipuli.retiisi.org.uk> (raw)
In-Reply-To: <20200723231549.GE21353@pendragon.ideasonboard.com>

Hi Laurent,

On Fri, Jul 24, 2020 at 02:15:49AM +0300, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Fri, Jul 24, 2020 at 01:22:59AM +0300, Sakari Ailus wrote:
> > On Fri, Jul 17, 2020 at 11:57:22PM +0300, Laurent Pinchart wrote:
> > > Hi Jacopo,
> > > 
> > > (CC'ing Sakari)
> > > 
> > > Thank you for the patch.
> > > 
> > > On Fri, Jul 17, 2020 at 03:28:54PM +0200, Jacopo Mondi wrote:
> > > > The value of the data-shift property solely depend on the selected
> > > > bus width and it's not freely configurable.
> > > > 
> > > > Remove it from the bindings document and update its users accordingly.
> > > 
> > > Hmmmm that's an interesting one. Sakari, what do you think ?
> > > 
> > > > Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > > > ---
> > > >  Documentation/devicetree/bindings/media/i2c/ov5640.yaml | 9 ---------
> > > >  arch/arm/boot/dts/stm32mp157c-ev1.dts                   | 1 -
> > > >  2 files changed, 10 deletions(-)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/media/i2c/ov5640.yaml b/Documentation/devicetree/bindings/media/i2c/ov5640.yaml
> > > > index 5e1662e848bd..ab700a1830aa 100644
> > > > --- a/Documentation/devicetree/bindings/media/i2c/ov5640.yaml
> > > > +++ b/Documentation/devicetree/bindings/media/i2c/ov5640.yaml
> > > > @@ -92,12 +92,6 @@ properties:
> > > >                parallel bus.
> > > >              enum: [8, 10]
> > > > 
> > > > -          data-shift:
> > > > -            description: |
> > > > -              Shall be set to <2> for 8 bits parallel bus (lines 9:2 are used) or
> > > > -              <0> for 10 bits parallel bus.
> > > > -            enum: [0, 2]
> > > 
> > > Should you document in the description of bus-width that data-shift is
> > > implied ?
> > 
> > The purpose of the datas-shift property is to convey how the parallel bus
> > lines are connected for a given bus width for devices where it is
> > configurable. As this device does not not support that, then indeed this
> > property is not relevant for the device IMO.
> 
> Could you elaborate on this ? I believe the case that Jacopo is
> describing connects D[9:2] from the sensor to D[7:0] of the receiver
> (Jacopo, could you confirm ?). Isn't that what data-shift is for ?

Yes, it is. But in this case what data-shift configures is not configurable
as such but defined by another configuration, making the data-shift
property redundant. We generally haven't documented redundant things in DT
bindings --- for instance data-lanes is documented in bindings only if it
is configurable.

That said, it'd be nice to say which pins are used on less than full width
busses.

-- 
Regards,

Sakari Ailus