netdev - Re: [PATCH v4 6/9] dt-bindings: display: hdmi-connector: Add DDC power supply

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Message-ID: <20190427190123.6aik7by3fgkyjmq7@core.my.home>
Date:   Sat, 27 Apr 2019 21:01:23 +0200
From:   Ondřej Jirman <megous@...ous.com>
To:     Rob Herring <robh@...nel.org>
Cc:     linux-sunxi <linux-sunxi@...glegroups.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v4 6/9] dt-bindings: display: hdmi-connector: Add DDC
 power supply

On Fri, Apr 26, 2019 at 03:02:50PM -0500, Rob Herring wrote:
> On Fri, Apr 26, 2019 at 2:20 PM Ondřej Jirman <megous@...ous.com> wrote:
> >
> > On Fri, Apr 26, 2019 at 01:23:37PM -0500, Rob Herring wrote:
> > > On Sat, Apr 13, 2019 at 06:54:15PM +0200, megous@...ous.com wrote:
> > > > From: Ondrej Jirman <megous@...ous.com>
> > > >
> > > > Some Allwinner SoC using boards (Orange Pi 3 for example) need to enable
> > > > on-board voltage shifting logic for the DDC bus to be usable. Use
> > > > ddc-supply on the hdmi-connector to model this.
> > > >
> > > > Add binding documentation for optional ddc-supply property.
> > > >
> > > > Signed-off-by: Ondrej Jirman <megous@...ous.com>
> > > > ---
> > > >  .../devicetree/bindings/display/connector/hdmi-connector.txt     | 1 +
> > > >  1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/display/connector/hdmi-connector.txt b/Documentation/devicetree/bindings/display/connector/hdmi-connector.txt
> > > > index 508aee461e0d..33085aeb0bb9 100644
> > > > --- a/Documentation/devicetree/bindings/display/connector/hdmi-connector.txt
> > > > +++ b/Documentation/devicetree/bindings/display/connector/hdmi-connector.txt
> > > > @@ -9,6 +9,7 @@ Optional properties:
> > > >  - label: a symbolic name for the connector
> > > >  - hpd-gpios: HPD GPIO number
> > > >  - ddc-i2c-bus: phandle link to the I2C controller used for DDC EDID probing
> > > > +- ddc-supply: the power supply for the DDC bus
> > >
> > > It's not just for DDC. It powers the chips in bridge dongles for
> > > example. Pretty much every diagram I find just calls it 5V or +5V.
> > >
> > > So how about '5V-supply' or 'v5V-supply'?
> >
> > Just to be sure, the schematic that inspired this change looks like this:
> >
> > https://megous.com/dl/tmp/33b2971de6943e9d.png
> >
> > HDMI-5V is always on, and what is really being enabled here are mosfets
> > connected to DDC_CEC_EN and not the HDMI-5V power supply. So in this case it
> > really is just for DDC. It is conceivable that some boards may need both to
> > enable 5V for HDMI circuitry and some separate power shifting logic for
> > DDC bus.
> 
> Okay, not what I thought you were defining. DDC_CEC_EN is a GPIO line?
> I wouldn't characterize this as a voltage rail, so I don't think it
> should be a supply. Perhaps 'ddc-en-gpios'?

Yes it's GPIO. I'll implement it as GPIO.

> We certainly want to make it clear this is not the 5V supply.

Right. Thank you for review.

regards,
	Ondrej

> Rob
> 
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> linux-arm-kernel@...ts.infradead.org
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