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From:   Amit Kucheria <amit.kucheria@verdurent.com>
Date:   Wed, 15 Jan 2020 11:28:02 +0530
Message-ID: <CAHLCerO1OARY9OMDpGudSfBdmtRfeP_pYaE9=-Sn-10ZVjgXKA@mail.gmail.com>
Subject: Re: [PATCH v3 1/6] thermal: brcmstb_thermal: Do not use DT coefficients
To:     Florian Fainelli <f.fainelli@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Markus Mayer <mmayer@broadcom.com>,
        "maintainer:BROADCOM STB AVS TMON DRIVER" 
        <bcm-kernel-feedback-list@broadcom.com>,
        Zhang Rui <rui.zhang@intel.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "open list:BROADCOM STB AVS TMON DRIVER" <linux-pm@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        "moderated list:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>
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On Wed, Jan 15, 2020 at 12:36 AM Florian Fainelli <f.fainelli@gmail.com> wrote:
>
> At the time the brcmstb_thermal driver and its binding were merged, the
> DT binding did not make the coefficients properties a mandatory one,
> therefore all users of the brcmstb_thermal driver out there have a non
> functional implementation with zero coefficients. Even if these
> properties were provided, the formula used for computation is incorrect.
>
> The coefficients are entirely process specific (right now, only 28nm is
> supported) and not board or SoC specific, it is therefore appropriate to
> hard code them in the driver given the compatibility string we are
> probed with which has to be updated whenever a new process is
> introduced.
>
> We remove the existing coefficients definition since subsequent patches
> are going to add support for a new process and will introduce new
> coefficients as well.
>
> Fixes: 9e03cf1b2dd5 ("thermal: add brcmstb AVS TMON driver")
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>

> ---
>  drivers/thermal/broadcom/brcmstb_thermal.c | 31 +++++++---------------
>  1 file changed, 9 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/thermal/broadcom/brcmstb_thermal.c b/drivers/thermal/broadcom/brcmstb_thermal.c
> index 5825ac581f56..680f1a070606 100644
> --- a/drivers/thermal/broadcom/brcmstb_thermal.c
> +++ b/drivers/thermal/broadcom/brcmstb_thermal.c
> @@ -49,7 +49,7 @@
>  #define AVS_TMON_TP_TEST_ENABLE                0x20
>
>  /* Default coefficients */
> -#define AVS_TMON_TEMP_SLOPE            -487
> +#define AVS_TMON_TEMP_SLOPE            487
>  #define AVS_TMON_TEMP_OFFSET           410040
>
>  /* HW related temperature constants */
> @@ -108,23 +108,12 @@ struct brcmstb_thermal_priv {
>         struct thermal_zone_device *thermal;
>  };
>
> -static void avs_tmon_get_coeffs(struct thermal_zone_device *tz, int *slope,
> -                               int *offset)
> -{
> -       *slope = thermal_zone_get_slope(tz);
> -       *offset = thermal_zone_get_offset(tz);
> -}
> -
>  /* Convert a HW code to a temperature reading (millidegree celsius) */
>  static inline int avs_tmon_code_to_temp(struct thermal_zone_device *tz,
>                                         u32 code)
>  {
> -       const int val = code & AVS_TMON_TEMP_MASK;
> -       int slope, offset;
> -
> -       avs_tmon_get_coeffs(tz, &slope, &offset);
> -
> -       return slope * val + offset;
> +       return (AVS_TMON_TEMP_OFFSET -
> +               (int)((code & AVS_TMON_TEMP_MAX) * AVS_TMON_TEMP_SLOPE));
>  }
>
>  /*
> @@ -136,20 +125,18 @@ static inline int avs_tmon_code_to_temp(struct thermal_zone_device *tz,
>  static inline u32 avs_tmon_temp_to_code(struct thermal_zone_device *tz,
>                                         int temp, bool low)
>  {
> -       int slope, offset;
> -
>         if (temp < AVS_TMON_TEMP_MIN)
> -               return AVS_TMON_TEMP_MAX; /* Maximum code value */
> -
> -       avs_tmon_get_coeffs(tz, &slope, &offset);
> +               return AVS_TMON_TEMP_MAX;       /* Maximum code value */
>
> -       if (temp >= offset)
> +       if (temp >= AVS_TMON_TEMP_OFFSET)
>                 return 0;       /* Minimum code value */
>
>         if (low)
> -               return (u32)(DIV_ROUND_UP(offset - temp, abs(slope)));
> +               return (u32)(DIV_ROUND_UP(AVS_TMON_TEMP_OFFSET - temp,
> +                                         AVS_TMON_TEMP_SLOPE));
>         else
> -               return (u32)((offset - temp) / abs(slope));
> +               return (u32)((AVS_TMON_TEMP_OFFSET - temp) /
> +                             AVS_TMON_TEMP_SLOPE);
>  }
>
>  static int brcmstb_get_temp(void *data, int *temp)
> --
> 2.17.1
>