linux-kernel - Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6

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Date:   Sat, 18 May 2019 01:27:39 +0800
From:   Frank Lee <tiny.windzz@...il.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     rui.zhang@...el.com, Eduardo Valentin <edubezval@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>, robh+dt@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>, catalin.marinas@....com,
        will.deacon@....com, David Miller <davem@...emloft.net>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan.Cameron@...wei.com,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        paulmck@...ux.ibm.com, Andy Gross <andy.gross@...aro.org>,
        olof@...om.net, bjorn.andersson@...aro.org,
        Jagan Teki <jagan@...rulasolutions.com>,
        marc.w.gonzalez@...e.fr, stefan.wahren@...e.com,
        enric.balletbo@...labora.com, Linux PM <linux-pm@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6

On Fri, May 17, 2019 at 3:36 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Fri, May 17, 2019 at 01:51:56AM +0800, Frank Lee wrote:
> > > > +struct sun50i_thermal_chip {
> > > > +     int     sensor_num;
> > > > +     int     offset;
> > > > +     int     scale;
> > > > +     int     ft_deviation;
> > > > +     int     temp_calib_base;
> > > > +     int     temp_data_base;
> > > > +     int     (*enable)(struct tsens_device *tmdev);
> > > > +     int     (*disable)(struct tsens_device *tmdev);
> > > > +};
> > >
> > > I'm not super fond of having a lot of quirks that are not needed. If
> > > we ever need those quirks when adding support for a new SoC, then
> > > yeah, we should totally have some, but only when and if it's needed.
> > >
> > > Otherwise, the driver is more complicated for no particular reason.
> >
> > This is unavoidable because of the difference in soc.
>
> I know, but this isn't my point.
>
> My point is that at this time of the driver development, we don't know
> what is going to be needed to support all of those SoCs.
>
> Some of the parameters you added might not be needed, some parameters
> might be missing, we don't know. So let's keep it simple for now.
>
> > > > +static int tsens_probe(struct platform_device *pdev)
> > > > +{
> > > > +     struct tsens_device *tmdev;
> > > > +     struct device *dev = &pdev->dev;
> > > > +     int ret;
> > > > +
> > > > +     tmdev = devm_kzalloc(dev, sizeof(*tmdev), GFP_KERNEL);
> > > > +     if (!tmdev)
> > > > +             return -ENOMEM;
> > > > +
> > > > +     tmdev->dev = dev;
> > > > +     tmdev->chip = of_device_get_match_data(&pdev->dev);
> > > > +     if (!tmdev->chip)
> > > > +             return -EINVAL;
> > > > +
> > > > +     ret = tsens_init(tmdev);
> > > > +     if (ret)
> > > > +             return ret;
> > > > +
> > > > +     ret = tsens_register(tmdev);
> > > > +     if (ret)
> > > > +             return ret;
> > > > +
> > > > +     ret = tmdev->chip->enable(tmdev);
> > > > +     if (ret)
> > > > +             return ret;
> > > >
> > > > +     platform_set_drvdata(pdev, tmdev);
> > >
> > > Your registration should be the very last thing you do. Otherwise, you
> > > have a small window where the get_temp callback can be called, but the
> > > driver will not be functional yet.
> >
> > No. Anyway, ths data qcquisition is ms level.
>
> That's kind of irrelevant. There's nothing preventing get_temp to be
> called right away.
As Ondřej said,

Registration after enabling will lead to call tz update on non-registered tz
from an interrupt handler.

>
> > > > +     ret = tsens_calibrate(tmdev);
> > > > +     if (ret)
> > > > +             return ret;
> > > > +
> > > > +     /*
> > > > +      * clkin = 24MHz
> > > > +      * T acquire = clkin / (SUN50I_THS_CTRL0_T_ACQ + 1)
> > > > +      *           = 20us
> > > > +      */
> > > > +     regmap_write(tmdev->regmap, SUN50I_THS_CTRL0,
> > > > +                  SUN50I_THS_CTRL0_T_ACQ(479));
> > > > +     /* average over 4 samples */
> > > > +     regmap_write(tmdev->regmap, SUN50I_H6_THS_MFC,
> > > > +                  SUN50I_THS_FILTER_EN |
> > > > +                  SUN50I_THS_FILTER_TYPE(1));
> > > > +     /* period = (SUN50I_H6_THS_PC_TEMP_PERIOD + 1) * 4096 / clkin; ~10ms */
> > > > +     regmap_write(tmdev->regmap, SUN50I_H6_THS_PC,
> > > > +                  SUN50I_H6_THS_PC_TEMP_PERIOD(58));
> > > > +     /* enable sensor */
> > > > +     val = GENMASK(tmdev->chip->sensor_num - 1, 0);
> > > > +     regmap_write(tmdev->regmap, SUN50I_H6_THS_ENABLE, val);
> > > > +
> > > > +     return 0;
> > > > +
> > > > +assert_reset:
> > > > +     reset_control_assert(tmdev->reset);
> > > > +
> > > > +     return ret;
> > >
> > > Can't we do that with runtime_pm?
> >
> > Saving energy doesn't make much sense compared to system security.
>
> I'm not sure what you mean by security.

Protect system hardware from damage.

Thx,
Yangtao
>
> Maxime
>
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com