linux-kernel - Re: [PATCH v3 16/24] drm/i2c: tda998x: add DT documentation

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Date:	Tue, 21 Jan 2014 10:17:56 -0800
From:	Olof Johansson <olof@...om.net>
To:	Jean-Francois Moine <moinejf@...e.fr>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 16/24] drm/i2c: tda998x: add DT documentation

On Mon, Jan 20, 2014 at 1:54 AM, Jean-Francois Moine <moinejf@...e.fr> wrote:
> On Sun, 19 Jan 2014 20:06:09 -0800
> Olof Johansson <olof@...om.net> wrote:
>
>> Hi,
>>
>> On Sun, Jan 19, 2014 at 10:58 AM, Jean-Francois Moine <moinejf@...e.fr> wrote:
>> > Signed-off-by: Jean-Francois Moine <moinejf@...e.fr>
>> > ---
>> >  .../devicetree/bindings/drm/i2c/tda998x.txt        | 24 ++++++++++++++++++++++
>> >  1 file changed, 24 insertions(+)
>> >  create mode 100644 Documentation/devicetree/bindings/drm/i2c/tda998x.txt
>>
>> Please cc bindings for review to devicetree@...r.kernel.org (cc:d here now)
>>
>> > diff --git a/Documentation/devicetree/bindings/drm/i2c/tda998x.txt b/Documentation/devicetree/bindings/drm/i2c/tda998x.txt
>> > new file mode 100644
>> > index 0000000..72da71d
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/drm/i2c/tda998x.txt
>> > @@ -0,0 +1,24 @@
>> > +Device-Tree bindings for the NXP TDA998x HDMI transmitter
>> > +
>> > +Required properties;
>> > +  - compatible: must be "nxp,tda998x"
>> > +
>> > +Optional properties:
>> > +  - interrupts: interrupt number for HDMI exchanges - default: by polling
>>
>> What are HDMI exchanges, and how do they differ from other interrupts?
>
> The used HDMI interrupt events are screen plug/unplug and EDID read.
> There are also CEC read/write which are not yet implemented in the
> tda998x driver.
>
> There is no difference from normal interrupts, except that the events
> may be get by polling, so, the interrupt number is optional.]

Ok, then it looks like the property description is a little confusing.
I'd remove the mentioning of HDMI exchanges from it.

>> > +
>> > +  - pinctrl-0: pin control group to be used for this controller (IRQ).
>> > +
>> > +  - pinctrl-names: must contain a "default" entry.
>> > +
>> > +  - video-ports: 24 bits value - default: <0x230145>
>>
>> What is this?
>
> The video-ports value defines how the video controller is connected to
> the tda998x chip. Each 4 bits value tells from which input pins comes
> the video data and if there is any bit inversion. Each byte of this
> video-ports is used to load the VIP_CNTRL_{0,1,2} registers. These ones
> are described in the TDA9983B documentation which is the closer
> available document about the TDA998x family.
>
> The default value is the one defined for TI boards.
> A known other value is <0x234501> which is used for Russell's Armada
> DRM driver in the Cubox (Marvell A510), but this driver has no DT
> support.

Ok, this is a classic case where the binding should describe how
things are configured/wired up instead of hardcoding a register value
like this. From the data sheet there seems to be a _lot_ of settings,
so selecting the needed subset for now might be acceptable (and go
with defaults on the rest).


-Olof
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