linux-kernel - Re: [PATCH v3 2/2] hwmon: pmbus: max20730: adjust the vout reading given voltage divider

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Date:   Tue, 29 Sep 2020 22:24:05 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Chu Lin <linchuyuan@...gle.com>
Cc:     jdelvare@...e.com, robh+dt@...nel.org, linux-hwmon@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        qiongwang@...gle.com, zhongqil@...gle.com, jasonling@...gle.com,
        belgaied@...gle.com
Subject: Re: [PATCH v3 2/2] hwmon: pmbus: max20730: adjust the vout reading
 given voltage divider

On Thu, Sep 24, 2020 at 09:54:44PM +0000, Chu Lin 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>
> ---

<Formletter>  
Change log goes here. If it is missing, I won't know what changed.
That means I will have to dig out older patch versions to compare.
That costs time and will hold up both this patch as well as all other
patches which I still have to review.

Please keep this in mind when submitting patch revisions without change log.
</Formletter>

Worse, this is v3, and I had given v2 a Reviewed-by: tag which was dropped.
This means I have to compare the two versions to figure out what changed,
probably just to find out that nothing has changed since v2.

Patches like this are the reason why various patches won't make it into
the next kernel release. Sorry, I just don't have as much time as people
seem to think I have.

Guenter

>  drivers/hwmon/pmbus/max20730.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/hwmon/pmbus/max20730.c b/drivers/hwmon/pmbus/max20730.c
> index a151a2b588a5..fbf2f1e6c969 100644
> --- a/drivers/hwmon/pmbus/max20730.c
> +++ b/drivers/hwmon/pmbus/max20730.c
> @@ -31,6 +31,7 @@ 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)
> @@ -114,6 +115,14 @@ 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 (ret > 0 && data->vout_voltage_divider[0] && data->vout_voltage_divider[1]) {
> +			u64 temp = DIV_ROUND_CLOSEST_ULL((u64)ret * data->vout_voltage_divider[1],
> +							 data->vout_voltage_divider[0]);
> +			ret = clamp_val(temp, 0, 0xffff);
> +		}
> +		break;
>  	default:
>  		ret = -ENODATA;
>  		break;
> @@ -364,6 +373,15 @@ 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)