[alsa-devel] [PATCH 2/2] sgtl5000.txt: Explain the required and optional power supplies

Matt Sealey matt at genesi-usa.com
Mon May 13 18:07:19 CEST 2013

I would say;

"VDDD is an optional supply and could be unconnected on designs. In
this case an internal regulator is used."

The original sentence has 'and' twice, which looks a little weird in
English. I will also advocate "could" instead of "can," since it's the
past tense (i.e. the board is already designed and we are merely
describing a board in the binding, not dictating design methodology in
the binding). That said,

Signed-off-by: Matt Sealey <matt at genesi-usa.com>

I have a question that is slightly related.

It is possible to direct the SGTL5000 VDDD charge pump source to VDDA
or VDDIO via CHIP_LINREG_CTRL. It is automatically set to the highest
voltage of VDDA/VDDIO (differing voltages) or VDDA (both the same and
higher than 3.1V) at "start."

It may be prudent for some boards that supply >3.1V to dictate
switching to VDDIO as the charge pump supply, and I wonder how we'd
actually define that. Supplying a regulator for VDDD and matching it
would not suit the case where a single 3.3V supply went to all
supplies (VDDD, VDDA, VDDIO) which I have seen. It would need a
property.. VDDD-source maybe?

If you were going for a low-noise design without a dedicated VDDD, I
would think you'd want to keep VDDA decoupled from the digital logic
and that isn't the default..

On Mon, May 13, 2013 at 10:39 AM, Fabio Estevam
<fabio.estevam at freescale.com> wrote:
> sgtl5000 has two power supplies that are mandatory: VDDA and VDDIO.
> VDDD is an optional supply and can be left unconnected and in this case an
> internal regulator is used.
> Signed-off-by: Fabio Estevam <fabio.estevam at freescale.com>
> ---
>  .../devicetree/bindings/sound/sgtl5000.txt         |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> diff --git a/Documentation/devicetree/bindings/sound/sgtl5000.txt b/Documentation/devicetree/bindings/sound/sgtl5000.txt
> index 9cc4444..3537a7d 100644
> --- a/Documentation/devicetree/bindings/sound/sgtl5000.txt
> +++ b/Documentation/devicetree/bindings/sound/sgtl5000.txt
> @@ -5,9 +5,19 @@ Required properties:
>  - reg : the I2C address of the device
> +- VDDA-supply: the regulator for VDDA supply
> +
> +- VDDIO-supply: the regulator for VDDIO supply
> +
> +Optional properties:
> +
> +- VDDD-supply: the regulator for VDDD supply
> +
>  Example:
>  codec: sgtl5000 at 0a {
>         compatible = "fsl,sgtl5000";
>         reg = <0x0a>;
> +       VDDA-supply = <&vdda_reg>;
> +       VDDIO-supply = <&vddio_reg>;
>  };
> --

Matt Sealey <matt at genesi-usa.com>
Product Development Analyst, Genesi USA, Inc.

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