linux-kernel - Re: [PATCH 2/2] iio: light: vcnl4000: Add ps high definition for vcnl4040

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Date: Mon, 18 Dec 2023 17:00:10 +0100
From: Mårten Lindahl <martenli@...s.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: linux-iio@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
 kernel@...s.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: light: vcnl4000: Add ps high definition for
 vcnl4040

On 12/18/23 16:19, Mårten Lindahl wrote:
> On 12/17/23 15:15, Jonathan Cameron wrote:
>> On Fri, 15 Dec 2023 13:43:05 +0100
>> Mårten Lindahl <marten.lindahl@...s.com> wrote:
>>
>>> The vcnl4040 proximity sensor defaults to 12 bit data resolution, but
>>> the chip also supports 16 bit data resolution, which is called 
>>> proximity
>>> high definition (PS_HD).
>>>
>>> Add read/write attribute for proximity resolution, and read attribute
>>> for available proximity resolution values for the vcnl4040 chip.
>>>
>>> Signed-off-by: Mårten Lindahl <marten.lindahl@...s.com>
> Hi Jonathan!
>> I'll review this on basis the usecase is clear (see reply to cover 
>> letter)
>
> I'll skip this patch (see reply to cover letter comment)
>
> Your are right about the paired register manipulation. Better to 
> read/write byte instead of word.

Hi Jonathan!

I now remember why the register is read as a word (CONF1/CONF2). It is 
addressed as one 16 bit register where CONF1 is the low 8 bit field and 
CONF2 is the high bit field. It is the same address/code for both:

Register PS_CONF1 - COMMAND CODE: 0x03_L (0x03 DATA BYTE LOW)

Register PS_CONF2 - COMMAND CODE: 0x03_H (0x03 DATA BYTE HIGH)

Where in my case (PS_CONF2->PS_HD[3] is the same as PS_CONF1[11])

Kind regards

Mårten

>
> Kind regards
>
> Mårten
>
>>
>> The manipulation of the CONF1 and CONF2 registers in a pair is rather 
>> odd given you
>> only want to change one bit here.
>>
>> Why is that done?
>>> ---
>>>   drivers/iio/light/vcnl4000.c | 87 
>>> +++++++++++++++++++++++++++++++++++++++++++-
>>>   1 file changed, 85 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/iio/light/vcnl4000.c 
>>> b/drivers/iio/light/vcnl4000.c
>>> index fdf763a04b0b..2addff635b79 100644
>>> --- a/drivers/iio/light/vcnl4000.c
>>> +++ b/drivers/iio/light/vcnl4000.c
>>> @@ -90,6 +90,7 @@
>>>   #define VCNL4040_PS_CONF1_PS_SHUTDOWN    BIT(0)
>>>   #define VCNL4040_PS_CONF2_PS_IT    GENMASK(3, 1) /* Proximity 
>>> integration time */
>>>   #define VCNL4040_CONF1_PS_PERS    GENMASK(5, 4) /* Proximity 
>>> interrupt persistence setting */
>>> +#define VCNL4040_PS_CONF2_PS_HD        BIT(11)    /* Proximity high 
>>> definition */
>>>   #define VCNL4040_PS_CONF2_PS_INT    GENMASK(9, 8) /* Proximity 
>>> interrupt mode */
>>>   #define VCNL4040_PS_CONF3_MPS        GENMASK(6, 5) /* Proximity 
>>> multi pulse number */
>>>   #define VCNL4040_PS_MS_LED_I        GENMASK(10, 8) /* Proximity 
>>> current */
>>> @@ -170,6 +171,11 @@ static const int vcnl4040_ps_calibbias_ua[][2] = {
>>>       {0, 200000},
>>>   };
>>>   +static const int vcnl4040_ps_resolutions[2] = {
>>> +    12,
>>> +    16
>>> +};
>>> +
>>>   static const int vcnl4040_als_persistence[] = {1, 2, 4, 8};
>>>   static const int vcnl4040_ps_persistence[] = {1, 2, 3, 4};
>>>   static const int vcnl4040_ps_oversampling_ratio[] = {1, 2, 4, 8};
>>> @@ -880,6 +886,54 @@ static ssize_t 
>>> vcnl4040_write_ps_calibbias(struct vcnl4000_data *data, int val)
>>>       return ret;
>>>   }
>>>   +static ssize_t vcnl4040_read_ps_resolution(struct vcnl4000_data 
>>> *data, int *val, int *val2)
>>> +{
>>> +    int ret;
>>> +
>>> +    ret = i2c_smbus_read_word_data(data->client, VCNL4200_PS_CONF1);
>> The field seems to be in PS_CONF2.  So you are reading a word and I 
>> guess that
>> gets you two registers.  Can we not do a byte read to get just CONF2?
>>> +    if (ret < 0)
>>> +        return ret;
>>> +
>>> +    ret = FIELD_GET(VCNL4040_PS_CONF2_PS_HD, ret);
>>> +    if (ret >= ARRAY_SIZE(vcnl4040_ps_resolutions))
>>> +        return -EINVAL;
>>> +
>>> +    *val = vcnl4040_ps_resolutions[ret];
>>> +    *val2 = 0;
>>> +
>>> +    return ret;
>>> +}
>>> +
>>> +static ssize_t vcnl4040_write_ps_resolution(struct vcnl4000_data 
>>> *data, int val)
>>> +{
>>> +    unsigned int i;
>>> +    int ret;
>>> +    u16 regval;
>>> +
>>> +    for (i = 0; i < ARRAY_SIZE(vcnl4040_ps_resolutions); i++) {
>>> +        if (val == vcnl4040_ps_resolutions[i])
>>> +            break;
>>> +    }
>>> +
>>> +    if (i >= ARRAY_SIZE(vcnl4040_ps_resolutions))
>>> +        return -EINVAL;
>>> +
>>> +    mutex_lock(&data->vcnl4000_lock);
>>> +
>>> +    ret = i2c_smbus_read_word_data(data->client, VCNL4200_PS_CONF1);
>>> +    if (ret < 0)
>>> +        goto out_unlock;
>>> +
>>> +    regval = (ret & ~VCNL4040_PS_CONF2_PS_HD);
>>> +    regval |= FIELD_PREP(VCNL4040_PS_CONF2_PS_HD, i);
>>> +    ret = i2c_smbus_write_word_data(data->client, VCNL4200_PS_CONF1,
>>> +                    regval);
>>> +
>>> +out_unlock:
>>> +    mutex_unlock(&data->vcnl4000_lock);
>>> +    return ret;
>>> +}
>> c),