Re: [v1 1/3] media: dt-bindings: ov8856: Document YAML bindings

From: Robert Foss <robert.foss@linaro.org>
To: Fabio Estevam <festevam@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Tomasz Figa <tfiga@chromium.org>,
	ben.kao@intel.com, Rob Herring <robh+dt@kernel.org>,
	linux-mediatek@lists.infradead.org,
	Dongchun Zhu <dongchun.zhu@mediatek.com>,
	Jonathan.Cameron@huawei.com,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	linux-media <linux-media@vger.kernel.org>
Subject: Re: [v1 1/3] media: dt-bindings: ov8856: Document YAML bindings
Date: Thu, 12 Mar 2020 11:13:59 +0100	[thread overview]
Message-ID: <CAG3jFytyTO9h311WzTGDwDzGF-rwY1ANC=mhXXGxn6v83Anqmw@mail.gmail.com> (raw)
In-Reply-To: <CAG3jFyuLMxUEr7yZAHT99JK8NoUZc-aquuMEtSBH_Vipa-_giQ@mail.gmail.com>

On Tue, 10 Mar 2020 at 16:51, Robert Foss <robert.foss@linaro.org> wrote:
>
> Hey Fabio,
>
> Thanks for having a look at this series so quickly.
>
> On Tue, 10 Mar 2020 at 14:57, Fabio Estevam <festevam@gmail.com> wrote:
> >
> > Hi Robert,
> >
> > On Tue, Mar 10, 2020 at 10:46 AM Robert Foss <robert.foss@linaro.org> wrote:
> >
> > > +    ov8856: camera-sensor@10 {
> > > +        compatible = "ovti,ov8856";
> > > +        reg = <0x10>;
> > > +        reset-gpios = <&pio 111 GPIO_ACTIVE_HIGH>;
> >
> > Could you double check this is correct? Other OmniVision sensors have
> > reset-gpios as active low.
>
> I have tested this, unfortunately I don't have access to a ov8856
> datasheet that includes
> this level of detail. But I have tested this.
>
> >
> > I suspect that the driver has also an inverted logic, so that's why it works.
>
> That could explain it still working. Let me have a look into the
> driver and see what it does.
>

I had a look at some of OmniVision drivers, and there does seem to be
a logical inversion in some of them,
but not all of them.

ov7251:
- enable-gpios: Chip enable GPIO. Polarity is GPIO_ACTIVE_HIGH. This corresponds
  to the hardware pin XSHUTDOWN which is physically active low.

ov5640:
- reset-gpios: reference to the GPIO connected to the reset pin, if any.
           This is an active low signal to the OV5640.

I think the confusion stems from the XSHUTDOWN pin being mapped to a
GPIO called reset, and the two being logically inverted. Currently
this series does several mappings.

XSHUTDOWN -> reset-gpio -> n_shutdn_gpio
       ^                           ^                      ^
Physical Pin               DT                Driver

I think changing to what ov5640 does makes the most sense.
XSHUTDOWN -> reset-gpio -> reset_gpio

> >
> > I don't have access to the datasheet though, so I am just guessing.
>
> Me neither unfortunately, if anyone does have a link for it, I would
> very much appreciate it.

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