Message-ID: <20130827152405.GQ19893@e106331-lin.cambridge.arm.com>
Date:	Tue, 27 Aug 2013 16:24:05 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Prabhakar Lad <prabhakar.csengg@...il.com>
Cc:	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	LMML <linux-media@...r.kernel.org>,
	DLOS <davinci-linux-open-source@...ux.davincidsp.com>,
	LKML <linux-kernel@...r.kernel.org>, devicetree@...r.kernel.org,
	LDOC <linux-doc@...r.kernel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Kumar Gala <galak@...eaurora.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>
Subject: Re: [PATCH v3 2/2] media: i2c: adv7343: add OF support

[fixing up devicetree list address]

On Mon, Aug 26, 2013 at 03:41:45AM +0100, Prabhakar Lad wrote:
> Hi Sylwester,
> 
> On Fri, Aug 23, 2013 at 11:33 PM, Sylwester Nawrocki
> <s.nawrocki@...sung.com> wrote:
> > Cc: DT binding maintainers

Cheers!

> >
> > On 07/20/2013 08:21 AM, Lad, Prabhakar wrote:
> >> From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
> >>
> >> add OF support for the adv7343 driver.
> >>
> >> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@...il.com>
> >> ---
> > [...]
> >>  .../devicetree/bindings/media/i2c/adv7343.txt      |   48 ++++++++++++++++++++
> >>  drivers/media/i2c/adv7343.c                        |   46 ++++++++++++++++++-
> >>  2 files changed, 93 insertions(+), 1 deletion(-)
> >>  create mode 100644 Documentation/devicetree/bindings/media/i2c/adv7343.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/media/i2c/adv7343.txt b/Documentation/devicetree/bindings/media/i2c/adv7343.txt
> >> new file mode 100644
> >> index 0000000..5653bc2
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/media/i2c/adv7343.txt
> >> @@ -0,0 +1,48 @@
> >> +* Analog Devices adv7343 video encoder
> >> +
> >> +The ADV7343 are high speed, digital-to-analog video encoders in a 64-lead LQFP
> >> +package. Six high speed, 3.3 V, 11-bit video DACs provide support for composite
> >> +(CVBS), S-Video (Y-C), and component (YPrPb/RGB) analog outputs in standard
> >> +definition (SD), enhanced definition (ED), or high definition (HD) video
> >> +formats.
> >> +
> >> +Required Properties :
> >> +- compatible: Must be "adi,adv7343"
> >> +
> >> +Optional Properties :
> >> +- adi,power-mode-sleep-mode: on enable the current consumption is reduced to
> >> +                           micro ampere level. All DACs and the internal PLL
> >> +                           circuit are disabled.

This seems to be a boolean property, and I couldn't find any description
in the linked datasheet of the constraints under which the unit may be
put into sleep mode.

Why do we require this property in the dt? Can the driver not always put
a adv734x into sleep mode if it wants to, and then wake it up as
required?

> >
> > Sorry for getting back so late to this. I realize this is already queued in
> > the media tree. But this binding doesn't look good enough to me. I think it
> > will need to be corrected during upcoming -rc period.
> >
> Thanks for the catch :-)
> 
> > It might be hard to figure out only from the chip's datasheet what
> > adi,power-mode-sleep-mode really refers to. AFAICS it is for assigning some
> > value to a specific register. If we really need to specify register values
> > in the device tree then it would probably make sense to describe to which
> > register this apply. Now the name looks like derived from some structure
> > member name in the Linux driver of the device.
> >
> the property is derived from the datasheet itself for example the
> 'adi,power-mode-sleep-mode' --> Register 0x0 power mode bit 0
> 'adi,power-mode-pll-ctrl' ---> Register 0x0 power mode bit 1
> 'adi,dac-enable' ----> Register 0x0 power mode bit 2-7
> 'adi,sd-dac-enable' ---> Register 0x82 SD mode register bit 1-2
> 
> [1] http://www.analog.com/static/imported-files/data_sheets/ADV7342_7343.pdf
> 
> >> +- adi,power-mode-pll-ctrl: PLL and oversampling control. This control allows
> >> +                        internal PLL 1 circuit to be powered down and the
> >> +                        oversampling to be switched off.

This affects whether or not oversampling is possible. That sounds like
it should be a run-time configurable rather than a fixed property of the
device.

> >
> > Similar comments applies to this property.
> >
> >> +- ad,adv7343-power-mode-dac: array configuring the power on/off DAC's 1..6,
> >> +                           0 = OFF and 1 = ON, Default value when this
> >> +                           property is not specified is <0 0 0 0 0 0>.
> >
> > Name of the property is incorrect here. It has changed to "adi,dac-enable".
> >
> OK

Why do we need this property at all? Might some DACs not be wired up to
anything?

Surely this could be configured at run-time as and when the user wants
to use the DACs.

> 
> >> +- ad,adv7343-sd-config-dac-out: array configure SD DAC Output's 1 and 2, 0 = OFF
> >> +                              and 1 = ON, Default value when this property is
> >> +                              not specified is <0 0>.
> >
> > Similarly, "adi,sd-dac-enable.
> >
> OK

Again, couldn't this be done at run-time?

Do we need to permanently disable/enable some DACs? If so, why?

I also note from the spec that the unit has two clocks, CLKIN_A and
CLKIN_B that aren't in the binding, but should be. Some regulators
too (VDD, PVDD, VAA, VDD_IO, VREF?).

Thanks,
Mark.
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