linux-kernel - Re: [PATCH v3 2/4] thermal: renesas: rzg3s: Add thermal driver for the Renesas RZ/G3S SoC

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Message-ID: <CAMuHMdUUNFo4pqbXh1xMatsv7T7cnq0SmDxM_o9em0=gpurdCA@mail.gmail.com>
Date: Wed, 26 Mar 2025 14:26:43 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Claudiu <claudiu.beznea@...on.dev>
Cc: rafael@...nel.org, daniel.lezcano@...aro.org, rui.zhang@...el.com, 
	lukasz.luba@....com, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	geert+renesas@...der.be, magnus.damm@...il.com, p.zabel@...gutronix.de, 
	linux-pm@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH v3 2/4] thermal: renesas: rzg3s: Add thermal driver for
 the Renesas RZ/G3S SoC

Hi Claudiu,

On Mon, 24 Mar 2025 at 14:57, Claudiu <claudiu.beznea@...on.dev> wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>
> The Renesas RZ/G3S SoC features a Thermal Sensor Unit (TSU) that reports
> the junction temperature. The temperature is reported through a dedicated
> ADC channel. Add a driver for the Renesas RZ/G3S TSU.
>
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> ---
>
> Changes in v3:
> - drop the runtime resume/suspend from rzg3s_thermal_get_temp(); this
>   is not needed as the temperature is read with ADC
> - opened the devres group id in rzg3s_thermal_probe() and rename
>   previsouly rzg3s_thermal_probe() to rzg3s_thermal_probe_helper(), to
>   have simpler code; this approach was suggested by Jonathan in [1];
>   as there is no positive feedback for the generic solution [2] this
>   looks currently the best approach

Thanks for the update!

> --- /dev/null
> +++ b/drivers/thermal/renesas/rzg3s_thermal.c

> +static int rzg3s_thermal_get_temp(struct thermal_zone_device *tz, int *temp)
> +{
> +       struct rzg3s_thermal_priv *priv = thermal_zone_device_priv(tz);
> +       int ts_code_ave = 0;
> +       int ret, val;
> +
> +       if (priv->mode != THERMAL_DEVICE_ENABLED)
> +               return -EAGAIN;
> +
> +       for (u8 i = 0; i < TSU_READ_STEPS; i++) {
> +               ret = iio_read_channel_raw(priv->channel, &val);
> +               if (ret < 0)
> +                       return ret;
> +
> +               ts_code_ave += val;
> +               /*
> +                * According to the HW manual (section 40.4.4 Procedure for Measuring the
> +                * Temperature) we need to wait here at leat 3us.
> +                */
> +               usleep_range(5, 10);
> +       }
> +
> +       ret = 0;
> +       ts_code_ave = DIV_ROUND_CLOSEST(MCELSIUS(ts_code_ave), TSU_READ_STEPS);
> +
> +       /*
> +        * According to the HW manual (section 40.4.4 Procedure for Measuring the Temperature)
> +        * the computation formula is as follows:
> +        *
> +        * Tj = (ts_code_ave - priv->calib1) * 165 / (priv->calib0 - priv->calib1) - 40
> +        *
> +        * Convert everything to mili Celsius before applying the formula to avoid

milli

> +        * losing precision.
> +        */
> +
> +       *temp = DIV_ROUND_CLOSEST((s64)(ts_code_ave - MCELSIUS(priv->calib1)) * MCELSIUS(165),
> +                                 MCELSIUS(priv->calib0 - priv->calib1)) - MCELSIUS(40);

This is a 64-by-32 division. When compile-testing on arm32:

rzg3s_thermal.c:(.text+0x330): undefined reference to `__aeabi_ldivmod'

> +
> +       /* Report it in mili degrees Celsius and round it up to 0.5 degrees Celsius. */

milli


> +       *temp = roundup(*temp, 500);
> +
> +       return ret;
> +}

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds