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From:   Amit Kucheria <amit.kucheria@verdurent.com>
Date:   Thu, 5 Dec 2019 00:31:11 +0530
Message-ID: <CAHLCerN0bJC0sMtZ2DneZSStkeTjQKHZeTNjJ4A31yV07hPb_A@mail.gmail.com>
Subject: Re: [PATCH 1/6] thermal: brcmstb_thermal: Do not use DT coefficients
To:     Florian Fainelli <f.fainelli@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Markus Mayer <mmayer@broadcom.com>,
        "maintainer:BROADCOM STB AVS TMON DRIVER" 
        <bcm-kernel-feedback-list@broadcom.com>,
        Zhang Rui <rui.zhang@intel.com>,
        Eduardo Valentin <edubezval@gmail.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        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, Dec 4, 2019 at 11:12 PM Florian Fainelli <f.fainelli@gmail.com> wrote:
>
> On 12/4/19 12:41 AM, Amit Kucheria wrote:
> > On Wed, Oct 30, 2019 at 11:51 PM 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")
> >
> > I think you should fix the computation formula as the first patch and
> > then merge the rest of this patch into your second patch.
> >
> > I don't think the intermediate state of converting named constants to
> > magic numbers is needed just to convert it over to another set of
> > parameters.
>
> ok, so you would rather see this patch using the defined constants while
> fixing the formula, and in a subsequent patch getting rid of the
> constant names since they are going to be added to a per-process table,
> does that sound reasonable?

Yes, that way the first patch would fix a bug (and with a Fixes tag
potentially gets backported to stable), the second would convert over
to the per-process table.

Regards,
Amit

> >
> > Regards,
> > Amit
> >
> >> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> >> ---
> >>  drivers/thermal/broadcom/brcmstb_thermal.c | 37 ++++------------------
> >>  1 file changed, 6 insertions(+), 31 deletions(-)
> >>
> >> diff --git a/drivers/thermal/broadcom/brcmstb_thermal.c b/drivers/thermal/broadcom/brcmstb_thermal.c
> >> index 5825ac581f56..42482af0422e 100644
> >> --- a/drivers/thermal/broadcom/brcmstb_thermal.c
> >> +++ b/drivers/thermal/broadcom/brcmstb_thermal.c
> >> @@ -48,15 +48,6 @@
> >>  #define AVS_TMON_TEMP_INT_CODE         0x1c
> >>  #define AVS_TMON_TP_TEST_ENABLE                0x20
> >>
> >> -/* Default coefficients */
> >> -#define AVS_TMON_TEMP_SLOPE            -487
> >> -#define AVS_TMON_TEMP_OFFSET           410040
> >> -
> >> -/* HW related temperature constants */
> >> -#define AVS_TMON_TEMP_MAX              0x3ff
> >> -#define AVS_TMON_TEMP_MIN              -88161
> >> -#define AVS_TMON_TEMP_MASK             AVS_TMON_TEMP_MAX
> >> -
> >>  enum avs_tmon_trip_type {
> >>         TMON_TRIP_TYPE_LOW = 0,
> >>         TMON_TRIP_TYPE_HIGH,
> >> @@ -108,23 +99,11 @@ 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 (410040 - (int)((code & 0x3FF) * 487));
> >>  }
> >>l
> >>  /*
> >> @@ -136,20 +115,16 @@ 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);
> >> +       if (temp < -88161)
> >> +               return 0x3FF;   /* Maximum code value */
> >>
> >> -       if (temp >= offset)
> >> +       if (temp >= 410040)
> >>                 return 0;       /* Minimum code value */
> >>
> >>         if (low)
> >> -               return (u32)(DIV_ROUND_UP(offset - temp, abs(slope)));
> >> +               return (u32)(DIV_ROUND_UP(410040 - temp, 487));
> >>         else
> >> -               return (u32)((offset - temp) / abs(slope));
> >> +               return (u32)((410040 - temp) / 487);
> >>  }
> >>
> >>  static int brcmstb_get_temp(void *data, int *temp)
> >> --
> >> 2.17.1
> >>
>
>
> --
> Florian