linux-kernel - Re: [v2 2/3] media: ov8856: Add devicetree support

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Message-ID: <20200326144725.GA2394@valkosipuli.retiisi.org.uk>
Date:   Thu, 26 Mar 2020 16:47:25 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Robert Foss <robert.foss@...aro.org>
Cc:     Dongchun Zhu <dongchun.zhu@...iatek.com>,
        Fabio Estevam <festevam@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Tomasz Figa <tfiga@...omium.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>
Subject: Re: [v2 2/3] media: ov8856: Add devicetree support

Hi Robert,

On Thu, Mar 26, 2020 at 12:56:37PM +0100, Robert Foss wrote:
...
> > > +static int __ov8856_power_on(struct ov8856 *ov8856)
> > > +{
> > > +     struct i2c_client *client = v4l2_get_subdevdata(&ov8856->sd);
> > > +     int ret;
> > > +
> > > +     ret = clk_prepare_enable(ov8856->xvclk);
> > > +     if (ret < 0) {
> > > +             dev_err(&client->dev, "failed to enable xvclk\n");
> > > +             return ret;
> > > +     }
> > > +
> > > +     gpiod_set_value_cansleep(ov8856->reset_gpio, GPIOD_OUT_HIGH);
> > > +
> > > +     ret = regulator_bulk_enable(ARRAY_SIZE(ov8856_supply_names),
> > > +                                 ov8856->supplies);
> > > +     if (ret < 0) {
> > > +             dev_err(&client->dev, "failed to enable regulators\n");
> > > +             goto disable_clk;
> > > +     }
> > > +
> > > +     gpiod_set_value_cansleep(ov8856->reset_gpio, GPIOD_OUT_LOW);
> > > +
> > > +     usleep_range(1500, 1800);
> >
> > I think you could omit the delay on ACPI based systems. Or just bail out
> > early in that case.
> 
> I'll add a check for reset_gpio being NULL, and skip the sleep for that case.

There could also be a regulator but no GPIO.

I think if you don't have either, then certainly there's no need for a
delay.

...

> > > +             ov8856->xvclk = NULL;
> > > +     } else if (IS_ERR(ov8856->xvclk)) {
> > > +             dev_err(&client->dev, "could not get xvclk clock (%ld)\n",
> > > +                     PTR_ERR(ov8856->xvclk));
> > > +             return PTR_ERR(ov8856->xvclk);
> > > +     }
> > > +
> > > +     ret = clk_set_rate(ov8856->xvclk, OV8856_XVCLK_24);
> >
> > This should either come from platform data, or perhaps it'd be even better
> > to get the clock rate and use assigned-clock-rates. I guess that's
> > preferred nowadays.
> 
> I'm a bit unsure about what this would look like.
> 
> Are you thinking something like the way ext_clk is used in smiapp_core.c?
> I went ahead and implemented support for retrieving and storing
> 'clock-rates' during the ov8856_check_hwcfg() call, and then setting
> the rate to the configured rate during probing.

With assigned-clock-rates, you can simply use clk_get_rate().

As you get the actual rate, it could be somewhat off of the intended one.

-- 
Kind regards,

Sakari Ailus