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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 7 Aug 2020 13:29:10 +0300
Message-ID: <CAHp75VcBa7kpmnHi84363pL-CHffSmYhObNa7r0t-g_rtmP++g@mail.gmail.com>
Subject: Re: [PATCH 2/2 resend] iio:temperature:mlx90632: Adding extended
 calibration option
To:     Crt Mori <cmo@melexis.com>
Cc:     Jonathan Cameron <jic23@kernel.org>,
        linux-iio <linux-iio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Aug 7, 2020 at 12:21 PM Crt Mori <cmo@melexis.com> wrote:

Oh yeah, you are right, there will be some comments :-)

> For some time market wants medical grade accuracy in medical range,

the market

> while still retaining the declared accuracy outside of the medical range
> within the same sensor. That is why we created extended calibration
> which is automatically switched to when object temperature is too high.
>
> This patch also introduces the object_ambient_temperature variable which
> is needed for more accurate calculation of the object infra-red
> footprint as sensor's ambient temperature might be totally different
> than what the ambient temperature is at object and that is why we can
> have some more error which can be eliminated. Currently this temperature

errors

> is fixed at 25, but interface to adjust it by user (with external sensor

the interface

> or just IR measurement of the another object which acts as ambient),

'of another' or 'the other' if we know what it is exactly.

> will be introduced in another commit.

...

>  struct mlx90632_data {
>         struct i2c_client *client;
>         struct mutex lock; /* Multiple reads for single measurement */
>         struct regmap *regmap;
>         u16 emissivity;

> +       u8 mtyp; /* measurement type - to enable extended range calculations */

Perhaps better to switch this struct to follow kernel doc in one of
preparatory patches and add the description of this field accordingly.

> +       u32 object_ambient_temperature;
>  };

...

> +static int mlx90632_set_meas_type(struct regmap *regmap, u8 type)
> +{
> +       int ret;
> +
> +       if ((type != MLX90632_MTYP_MEDICAL) & (type != MLX90632_MTYP_EXTENDED))
> +               return -EINVAL;

Not sure I understand the point of & vs. && here.

> +       ret = regmap_write(regmap, MLX90632_REG_I2C_CMD, MLX90632_RESET_CMD);
> +       if (ret < 0)
> +               return ret;
> +
> +       ret = regmap_write_bits(regmap, MLX90632_REG_CONTROL,
> +                                (MLX90632_CFG_MTYP_MASK | MLX90632_CFG_PWR_MASK),
> +                                (MLX90632_MTYP_STATUS(type) | MLX90632_PWR_STATUS_HALT));
> +       if (ret < 0)
> +               return ret;
> +
> +       mlx90632_pwr_continuous(regmap);

> +
> +       return ret;

Since you are using ' < 0' above and below (and I think it doesn't
worth it, i.o.w. you may drop them) here is something interesting
might be returned (actually not, see first part of this sentence).
Should be

return 0;

> +}

...

> +static int mlx90632_read_ambient_raw_extended(struct regmap *regmap,
> +                                             s16 *ambient_new_raw, s16 *ambient_old_raw)
> +{

> +       int ret;
> +       unsigned int read_tmp;

Please keep them in reversed xmas tree format.

> +
> +       ret = regmap_read(regmap, MLX90632_RAM_3(17), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       *ambient_new_raw = (s16)read_tmp;
> +
> +       ret = regmap_read(regmap, MLX90632_RAM_3(18), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       *ambient_old_raw = (s16)read_tmp;

> +       return ret;

Same comments as per previous function.

> +}

> +static int mlx90632_read_object_raw_extended(struct regmap *regmap, s16 *object_new_raw)
> +{
> +       int ret;
> +       unsigned int read_tmp;
> +       s32 read;

Besides all above comments being applicable here...

> +       ret = regmap_read(regmap, MLX90632_RAM_1(17), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       read = (s16)read_tmp;
> +
> +       ret = regmap_read(regmap, MLX90632_RAM_2(17), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       read = read - (s16)read_tmp;

...I'm wondering if you can use bulk reads of those registers.
Also I'm not sure you need explicit castings.

> +       ret = regmap_read(regmap, MLX90632_RAM_1(18), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       read = read - (s16)read_tmp;
> +
> +       ret = regmap_read(regmap, MLX90632_RAM_2(18), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       read = (read + (s16)read_tmp) / 2;

Ditto.

> +       ret = regmap_read(regmap, MLX90632_RAM_1(19), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       read = read + (s16)read_tmp;
> +
> +       ret = regmap_read(regmap, MLX90632_RAM_2(19), &read_tmp);
> +       if (ret < 0)
> +               return ret;
> +       read = read + (s16)read_tmp;

> +       if (read > 32767 || read < -32768)

These are defined as S16_MIN and S16_MAX. Use limits.h.

> +               return -EINVAL;

-ERANGE

> +       *object_new_raw = (int16_t)read;

Oh, no. Please avoid user space types in the kernel. And what's the
point anyway after checking the range?

> +       return ret;
> +}

...

> +static int mlx90632_read_all_channel_extended(struct mlx90632_data *data, s16 *object_new_raw,
> +                                             s16 *ambient_new_raw, s16 *ambient_old_raw)
> +{
> +       s32 ret;
> +       int tries = 4;
> +
> +       mutex_lock(&data->lock);
> +       ret = mlx90632_set_meas_type(data->regmap, MLX90632_MTYP_EXTENDED);
> +       if (ret < 0)
> +               goto read_unlock;


> +       while (tries-- > 0) {
> +               ret = mlx90632_perform_measurement(data);
> +               if (ret < 0)
> +                       goto read_unlock;
> +

> +               if (ret == 19)

It's funny. What does this magic mean?

> +                       break;
> +       }
> +       if (tries < 0) {
> +               ret = -ETIMEDOUT;
> +               goto read_unlock;
> +       }

Timeout loops are much better in a following style

unsigned int iterations = 4;

do {
  ...
} while (--iterations);
if (!iterations) {
  ...-ETIMEDOUT...
}

Besides that consider the iopoll.h APIs, perhaps it may be applied here.

> +       ret = mlx90632_read_object_raw_extended(data->regmap, object_new_raw);
> +       if (ret < 0)
> +               goto read_unlock;
> +
> +       ret = mlx90632_read_ambient_raw_extended(data->regmap, ambient_new_raw, ambient_old_raw);
> +
> +read_unlock:
> +       (void) mlx90632_set_meas_type(data->regmap, MLX90632_MTYP_MEDICAL);
> +
> +       mutex_unlock(&data->lock);
> +       return ret;
> +}

...

> +static s64 mlx90632_preprocess_temp_obj_extended(s16 object_new_raw, s16 ambient_new_raw,
> +                                                s16 ambient_old_raw, s16 Ka)
> +{
> +       s64 VR_IR, kKa, tmp;
> +
> +       kKa = ((s64)Ka * 1000LL) >> 10ULL;
> +       VR_IR = (s64)ambient_old_raw * 1000000LL +
> +               kKa * div64_s64(((s64)ambient_new_raw * 1000LL),
> +                       (MLX90632_REF_3));

And the point of using parentheses? It's not a Lisp language :-)
(Applicable everywhere in your code, the rule of thumb that any
particular comment given by reviewer should be considered against
entire code where it's appropriate)

> +       tmp = div64_s64(
> +                       div64_s64((((s64)object_new_raw) * 1000000000000LL), MLX90632_REF_12),
> +                       VR_IR);
> +       return div64_s64((tmp << 19ULL), 1000LL);
> +}

...

> +       TAdut = div64_s64(((ambient - kTA0) * 1000000LL), kTA) + 25 * 1000000LL;
> +       Tr4 = (div64_long(reflected, 10) + 27315) *
> +               (div64_long(reflected, 10) + 27315) *
> +               (div64_long(reflected, 10) + 27315) *
> +               (div64_long(reflected, 10) + 27315);
> +       TAdut4 = (div64_s64(TAdut, 10000LL) + 27315) *
> +               (div64_s64(TAdut, 10000LL) + 27315) *
> +               (div64_s64(TAdut, 10000LL)  + 27315) *
> +               (div64_s64(TAdut, 10000LL) + 27315);

Okay, looking at this I definitely think that this patch should be
split into a few smaller logically separated pieces like introducing
some helpers to calculate above with them.

...

> +       mlx90632->object_ambient_temperature = 25000; /* 25 degrees Celsius */

Comment is lying. milliCelsius.

-- 
With Best Regards,
Andy Shevchenko