linux-kernel - Re: [PATCH 1/2] iio: max597x: Add support for max597x

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Date:   Thu, 23 Mar 2023 06:07:36 -0700
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Naresh Solanki <naresh.solanki@...ements.com>,
        Lee Jones <lee@...nel.org>, Jonathan Cameron <jic23@...nel.org>
Cc:     Patrick Rudolph <patrick.rudolph@...ements.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH 1/2] iio: max597x: Add support for max597x

On 3/23/23 05:01, Naresh Solanki wrote:
> Hi,
>
> On 22-03-2023 09:28 pm, Lars-Peter Clausen wrote:
>> Hi,
>>
>> This looks really good. A few minor comments inline.
>>
>> On 3/22/23 05:43, Naresh Solanki wrote:
>>> [...]
>>> +static int max597x_iio_read_raw(struct iio_dev *iio_dev,
>>> +                struct iio_chan_spec const *chan,
>>> +                int *val, int *val2, long info)
>>> +{
>>> +    int ret;
>>> +    struct max597x_iio *data = iio_priv(iio_dev);
>>> +    unsigned int reg_l, reg_h;
>>> +
>>> +    switch (info) {
>>> +    case IIO_CHAN_INFO_RAW:
>>> +        ret = regmap_read(data->regmap, chan->address, &reg_l);
>>> +        if (ret < 0)
>>> +            return ret;
>>> +        ret = regmap_read(data->regmap, chan->address - 1, &reg_h);
>>> +        if (ret < 0)
>>> +            return ret;
>> Is there any chance of a race condition of getting inconsistent data 
>> when splitting this over two reads? I.e. registers being updated with 
>> new values in between the two reads.
> yes, reg_l holds lower 2 bits. due to latency in reads, value may differ.
>>> +        *val = (reg_h << 2) | (reg_l & 3);
>>> +
>>> +        return IIO_VAL_INT;
>>> +    case IIO_CHAN_INFO_SCALE:
>>> +
>>> +        switch (chan->address) {
>>> +        case MAX5970_REG_CURRENT_L(0):
>>> +            fallthrough;
>>
>> `fallthrough` should not be needed for multiple case statements right 
>> on top of each other with no code in between. Same below
> Sure.
>>
>>> +        case MAX5970_REG_CURRENT_L(1):
>>> +            /* in A, convert to mA */
>>> +            *val = data->irng[chan->channel] * 1000;
>>> +            *val2 =
>>> +                data->shunt_micro_ohms[chan->channel] * ADC_MASK;
>> ADC_MASK should really have a MAX5970_ prefix, but I guess it is 
>> defined in max597x.h
> Yes its taken from max597x.h
>>> +            return IIO_VAL_FRACTIONAL;
>>> +
>>> +        case MAX5970_REG_VOLTAGE_L(0):
>>> +            fallthrough;
>>> +        case MAX5970_REG_VOLTAGE_L(1):
>>> +            /* in uV, convert to mV */
>>> +            *val = data->mon_rng[chan->channel];
>>> +            *val2 = ADC_MASK * 1000;
>>> +            return IIO_VAL_FRACTIONAL;
>>> +        }
>>> +
>>> +        break;
>>> +    }
>>> +    return -EINVAL;
>>> +}
>>> [..]
>>> +static int max597x_iio_probe(struct platform_device *pdev)
>>> +{
>>> +    struct max597x_data *max597x = dev_get_drvdata(pdev->dev.parent);
>>> +    struct i2c_client *i2c = to_i2c_client(pdev->dev.parent);
>>> +    struct regmap *regmap = dev_get_regmap(pdev->dev.parent, NULL);
>>> +    struct iio_dev *indio_dev;
>>> +    struct max597x_iio *priv;
>>> +    int ret, i;
>>> +
>>> +    if (!regmap)
>>> +        return -EPROBE_DEFER;
>>> +
>>> +    if (!max597x || !max597x->num_switches)
>>> +        return -EPROBE_DEFER;
>>> +
>>> +    /* registering iio */
>>> +    indio_dev = devm_iio_device_alloc(&i2c->dev, sizeof(*priv));
>> For the devm allocations we should be using &pdev->dev and not the 
>> I2C device, since this is the device to which the allocations belong 
>> and where they should be freed when the device is removed.
> Sure. Will use &pdev->dev
>>> +    if (!indio_dev) {
>>> +        dev_err(&i2c->dev, "failed allocating iio device\n");
>> Consider using dev_err_probe() for error message printing. This will 
>> give a consistent formatting of the messages. Also again use 
>> &pdev->dev instead of I2C device to get the right device listed in 
>> the error messages.
> Sure. Will use
> dev_err_probe(&pdev->dev, ret, "could not register iio device");
>>> +        return -ENOMEM;
>>> +    }
>>> +    indio_dev->name = dev_name(&i2c->dev);
>> The IIO ABI wants the type of the chip for the name. E.g. "max5970", 
>> using dev_name() of the parent I2C device will result in something else.
> Sure. Will make it:
> indio_dev->name = dev_name(&pdev->dev);
>
dev_name() in general should not be used for indio_dev->name, it does 
not meet the ABI requirements for the IIO ABI. Move this into the switch 
block below and then assign "max5970" or "max5978" depending on the 
device type.