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From: Tomasz Figa <tfiga@chromium.org>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Sakari Ailus" <sakari.ailus@linux.intel.com>,
	"Dongchun Zhu" <dongchun.zhu@mediatek.com>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Bartosz Golaszewski" <bgolaszewski@baylibre.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Nicolas Boichat" <drinkcat@chromium.org>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Cao Bing Bu" <bingbu.cao@intel.com>,
	srv_heupstream <srv_heupstream@mediatek.com>,
	"moderated list:ARM/Mediatek SoC support"
	<linux-mediatek@lists.infradead.org>,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,"
	<linux-arm-kernel@lists.infradead.org>,
	"Sj Huang" <sj.huang@mediatek.com>,
	"Linux Media Mailing List" <linux-media@vger.kernel.org>,
	linux-devicetree <devicetree@vger.kernel.org>,
	"Louis Kuo" <louis.kuo@mediatek.com>,
	"Shengnan Wang (王圣男)" <shengnan.wang@mediatek.com>
Subject: Re: [PATCH V11 2/2] media: i2c: ov02a10: Add OV02A10 image sensor driver
Date: Tue, 30 Jun 2020 16:40:12 +0200
Message-ID: <CAAFQd5CwwLzGKiCPdd_EzipmXPA2aYBrk0QRPv6Bacy++tXrHA@mail.gmail.com> (raw)
In-Reply-To: <20200630143705.GW3703480@smile.fi.intel.com>

On Tue, Jun 30, 2020 at 4:37 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Tue, Jun 30, 2020 at 04:21:31PM +0200, Tomasz Figa wrote:
> > On Tue, Jun 30, 2020 at 4:19 PM Tomasz Figa <tfiga@chromium.org> wrote:
> > > On Tue, Jun 30, 2020 at 11:54 AM Sakari Ailus
> > > <sakari.ailus@linux.intel.com> wrote:
>
> ...
>
> > > > > +     ov02a10->rst_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
> > > >
> > > >
> > > > Shouldn't this be GPIOD_OUT_HIGH? That's the state it'll be after powering
> > > > the sensor off the first time. Alternatively make reset signal high in
> > > > runtime suspend callback.
> > >
> > > We might want to keep the signals low when the regulators are powered
> > > down, to reduce the leakage.
> >
> > Ah, I actually recall that the reset pin was physically active low, so
> > we would indeed better keep it at HIGH. Sorry for the noise.
>
> Here HIGH means "asserted", so in the code above it's LOW, means "deasserted",
> i.o.w. non-reset state. I dunno what is better, it depends to the firmware /
> driver expectations of the device configuration (from the power point of view,
> HIGH makes sense here, and not LOW, i.o.w. asserted reset line).
>
> And nice of the logical state that it doesn't depend to the active low / high
> (the latter just transparent to the user).

Yeah, after reading through the GPIO subsystem documentation and
discussing with a bunch of people on how to interpret it, we concluded
that the driver needs to deal only with the logical state of the
signal.

Actually, I later realized that the problem of leakage should likely
be solved by pinctrl suspend settings, based on given hardware
conditions, rather than the driver explicitly.

Best regards,
Tomasz

  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-30  2:49 [PATCH V11 0/2] media: i2c: Add support for 0V02A10 sensor Dongchun Zhu
2020-06-30  2:49 ` [PATCH V11 1/2] media: dt-bindings: media: i2c: Document OV02A10 bindings Dongchun Zhu
2020-06-30 16:59   ` Tomasz Figa
2020-06-30  2:49 ` [PATCH V11 2/2] media: i2c: ov02a10: Add OV02A10 image sensor driver Dongchun Zhu
2020-06-30  9:54   ` Sakari Ailus
2020-06-30 14:19     ` Tomasz Figa
2020-06-30 14:21       ` Tomasz Figa
2020-06-30 14:37         ` Andy Shevchenko
2020-06-30 14:40           ` Tomasz Figa [this message]
2020-07-01  7:58             ` Dongchun Zhu
2020-06-30 17:07   ` Tomasz Figa
2020-06-30 18:47     ` Sakari Ailus
2020-07-01  8:47       ` Dongchun Zhu
2020-07-01  9:00         ` Sakari Ailus

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