linux-kernel - Re: [PATCH] hwmon: pmbus: max20730: adjust the vout reading given voltage divider

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Message-ID: <CAKCA56CVHDDk0FDuda143L=_OXQ5JyWA=joKtKq-ok+R6JSYRg@mail.gmail.com>
Date:   Thu, 10 Sep 2020 10:20:15 -0700
From:   Chu Lin <linchuyuan@...gle.com>
To:     Chu Lin <linchuyuan@...gle.com>, jdelvare@...e.com,
        Guenter Roeck <linux@...ck-us.net>,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        Qiong Wang <qiongwang@...gle.com>,
        Zhongqi Li <zhongqil@...gle.com>,
        Jason Ling <jasonling@...gle.com>,
        Kais Belgaied <belgaied@...gle.com>
Subject: Re: [PATCH] hwmon: pmbus: max20730: adjust the vout reading given
 voltage divider

The same patch got sent twice. Please, discard this one.

Thanks,
Chu

On Thu, Sep 10, 2020 at 10:09 AM Chu Lin <linchuyuan@...gle.com> wrote:
>
> Problem:
> We use voltage dividers so that the voltage presented at the voltage
> sense pins is confusing. We might need to convert these readings to more
> meaningful readings given the voltage divider.
>
> Solution:
> Read the voltage divider resistance from dts and convert the voltage
> reading to a more meaningful reading.
>
> Testing:
> max20730 with voltage divider
>
> Signed-off-by: Chu Lin <linchuyuan@...gle.com>
> ---
>  drivers/hwmon/pmbus/max20730.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/drivers/hwmon/pmbus/max20730.c b/drivers/hwmon/pmbus/max20730.c
> index c0bb05487e0e..4b56810fa894 100644
> --- a/drivers/hwmon/pmbus/max20730.c
> +++ b/drivers/hwmon/pmbus/max20730.c
> @@ -29,6 +29,7 @@ struct max20730_data {
>         struct pmbus_driver_info info;
>         struct mutex lock;      /* Used to protect against parallel writes */
>         u16 mfr_devset1;
> +       u32 vout_voltage_divider[2];
>  };
>
>  #define to_max20730_data(x)  container_of(x, struct max20730_data, info)
> @@ -111,6 +112,12 @@ static int max20730_read_word_data(struct i2c_client *client, int page,
>                 max_c = max_current[data->id][(data->mfr_devset1 >> 5) & 0x3];
>                 ret = val_to_direct(max_c, PSC_CURRENT_OUT, info);
>                 break;
> +       case PMBUS_READ_VOUT:
> +               ret = pmbus_read_word_data(client, page, phase, reg);
> +               if (data->vout_voltage_divider[0] && data->vout_voltage_divider[1])
> +                       ret = DIV_ROUND_CLOSEST(ret * data->vout_voltage_divider[1],
> +                                               data->vout_voltage_divider[0]);
> +               break;
>         default:
>                 ret = -ENODATA;
>                 break;
> @@ -329,6 +336,15 @@ static int max20730_probe(struct i2c_client *client,
>         data->id = chip_id;
>         mutex_init(&data->lock);
>         memcpy(&data->info, &max20730_info[chip_id], sizeof(data->info));
> +       if (of_property_read_u32_array(client->dev.of_node, "vout-voltage-divider",
> +                                      data->vout_voltage_divider,
> +                                      ARRAY_SIZE(data->vout_voltage_divider)) != 0)
> +               memset(data->vout_voltage_divider, 0, sizeof(data->vout_voltage_divider));
> +       if (data->vout_voltage_divider[1] < data->vout_voltage_divider[0]) {
> +               dev_err(dev,
> +                       "The total resistance of voltage divider is less than output resistance\n");
> +               return -ENODEV;
> +       }
>
>         ret = i2c_smbus_read_word_data(client, MAX20730_MFR_DEVSET1);
>         if (ret < 0)
> --
> 2.28.0.526.ge36021eeef-goog
>