linux-kernel - Re: [v1 2/3] media: ov8856: Add devicetree support

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Message-ID: <20200311161654.GK2619@valkosipuli.retiisi.org.uk>
Date:   Wed, 11 Mar 2020 18:16:54 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Robert Foss <robert.foss@...aro.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        ben.kao@...el.com, Rob Herring <robh+dt@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org,
        Dongchun Zhu <dongchun.zhu@...iatek.com>,
        Tomasz Figa <tfiga@...omium.org>
Subject: Re: [v1 2/3] media: ov8856: Add devicetree support

On Wed, Mar 11, 2020 at 02:32:30PM +0100, Robert Foss wrote:
> Hey Sakari,
> 
> On Wed, 11 Mar 2020 at 12:49, Sakari Ailus <sakari.ailus@....fi> wrote:
> >
> > Hi Robert,
> >
> > On Tue, Mar 10, 2020 at 04:55:20PM +0100, Robert Foss wrote:
> > > Hi Andy,
> > >
> > > On Tue, 10 Mar 2020 at 15:26, Andy Shevchenko
> > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > >
> > > > On Tue, Mar 10, 2020 at 02:46:02PM +0100, Robert Foss wrote:
> > > > > Add devicetree match table, and enable ov8856_probe()
> > > > > to initialize power, clocks and reset pins.
> > > >
> > > > ...
> > > >
> > > > > +#define OV8856_NUM_SUPPLIES ARRAY_SIZE(ov8856_supply_names)
> > > >
> > > > Use ARRAY_SIZE() directly.
> > >
> > > Ack.
> > >
> > > >
> > > > Have you seen Sakari's comments?
> > > > Sakari, do I have déją vu or you indeed commented this driver?
> > >
> > > Yes, I may have missed some part of it, so please tell me if I have.
> > >
> > > There is a patchset floating around that implements a larger chunk of
> > > functionality,
> > > including a couple of new modes. This is based on that series.
> >
> > Please see earlier comments given against an earlier variant of this set.
> > They're on LMML.
> >
> > >
> > > >
> > > > ...
> > > >
> > > > > +     gpiod_set_value_cansleep(ov8856->n_shutdn_gpio, GPIOD_OUT_LOW);
> > > >
> > > > > +     gpiod_set_value_cansleep(ov8856->n_shutdn_gpio, GPIOD_OUT_HIGH);
> > > >
> > > > Yes, seems this one is inverted.
> > > >
> > > > ...
> > > >
> > > > > +{
> > > > > +     gpiod_set_value_cansleep(ov8856->n_shutdn_gpio, GPIOD_OUT_LOW);
> > > > > +     regulator_bulk_disable(OV8856_NUM_SUPPLIES, ov8856->supplies);
> > > > > +     clk_disable_unprepare(ov8856->xvclk);
> > > > > +}
> > > > > +
> > > > > +
> > > >
> > > > One blank line is enough.
> > > >
> > > > ...
> > > >
> > > > > +     ov8856->xvclk = devm_clk_get(&client->dev, "xvclk");
> > > > > +     if (IS_ERR(ov8856->xvclk)) {
> > > > > +             dev_err(&client->dev, "failed to get xvclk\n");
> > > > > +             return -EINVAL;
> > > > > +     }
> > > >
> > > > Previously it worked without clock provider, now you make a dependency.
> > > >
> > > > This won't work.
> > >
> > > So the ideal behavior would be to only use the xclk if it is provided?
> >
> > See e.g. the smiapp driver on how to do this so it continues to work on
> > ACPI.
> 
> Thanks for the pointer!
> 
> >
> > I think it'd be also appropriate to add the usleep() after lifting reset
> > only if the reset GPIO is defined for the device.
> 
> Ack

On second thought, that probably applies if any of the resources needed for
powering the device on are defined. It could be that there's no reset GPIO
but a regulator is still there, in which case a delay is needed.

-- 
Sakari Ailus