linux-kernel - Re: [PATCH 3/4] [media] ad5820: DT new optional field enable-gpios

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Date:   Thu, 20 Sep 2018 23:23:43 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Cc:     Pavel Machek <pavel@....cz>, Sakari Ailus <sakari.ailus@....fi>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hans Verkuil <hans.verkuil@...co.com>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 3/4] [media] ad5820: DT new optional field enable-gpios

On Thursday, 20 September 2018 23:21:28 EEST Laurent Pinchart wrote:
> Hi Ricardo,
> 
> Thank you for the patch.
> 
> On Thursday, 20 September 2018 19:19:11 EEST Ricardo Ribalda Delgado wrote:
> > Document new enable-gpio field. It can be used to disable the part
> > without turning down its regulator.
> > 
> > Cc: devicetree@...r.kernel.org
> > Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> > ---
> > 
> >  Documentation/devicetree/bindings/media/i2c/ad5820.txt | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/media/i2c/ad5820.txt
> > b/Documentation/devicetree/bindings/media/i2c/ad5820.txt index
> > 5940ca11c021..07d577bb37f7 100644
> > --- a/Documentation/devicetree/bindings/media/i2c/ad5820.txt
> > +++ b/Documentation/devicetree/bindings/media/i2c/ad5820.txt
> > 
> > @@ -8,6 +8,11 @@ Required Properties:
> >    - VANA-supply: supply of voltage for VANA pin
> > 
> > +Optional properties:
> > +
> > +   - enable-gpios : GPIO spec for the XSHUTDOWN pin.
> 
> xshutdown is active-low, so enable is active-high. Should this be documented
> explicitly, to avoid polarity errors ? Maybe something along the lines of
> 
> - enable-gpios: GPIO spec for the XSHUTDOWN pin. Note that the polarity of
> the enable GPIO is the opposite of the XSHUTDOWN pin (asserting the enable
> GPIO deasserts the XSHUTDOWN signal and vice versa).

Or alternatively you could name the property xshutdown-gpios, as explained in 
my (incorrect) review of 2/4.

> > If specified, it will be
> > +     asserted when VANA-supply is enabled.
> 
> That documents a driver behaviour, is it needed in DT ?
> 
> >  Example:
> >         ad5820: coil@c {
> > 
> > @@ -15,5 +20,6 @@ Example:
> >                 reg = <0x0c>;
> >                 VANA-supply = <&vaux4>;
> > 
> > +               enable-gpios = <&msmgpio 26 GPIO_ACTIVE_HIGH>;
> >         };


-- 
Regards,

Laurent Pinchart