linux-kernel - Re: [PATCH v6 3/3] hwmon: (adt7475) Add support for configuring initial PWM state

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Message-ID: <c261c74f-6829-4888-9836-6f27ba87dc25@alliedtelesis.co.nz>
Date: Mon, 22 Jul 2024 16:09:46 +1200
From: Chris Packham <chris.packham@...iedtelesis.co.nz>
To: Guenter Roeck <linux@...ck-us.net>, jdelvare@...e.com, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, ukleinek@...nel.org
Cc: linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v6 3/3] hwmon: (adt7475) Add support for configuring
 initial PWM state


On 22/07/24 15:53, Guenter Roeck wrote:
> On 7/21/24 17:58, Chris Packham wrote:
>> By default the PWM duty cycle in hardware is 100%. On some systems this
>> can cause unwanted fan noise. Add the ability to specify the fan
>> connections and initial state of the PWMs via device properties.
>>
>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>> ---
>>
>> Notes:
>>      Changes in v6:
>>      - Use do_div() instead of plain /
>>      - Use a helper function to avoid repetition between the of and 
>> non-of
>>        code paths.
>>      Changes in v5:
>>      - Deal with PWM frequency and duty cycle being specified in 
>> nanoseconds
>>      Changes in v4:
>>      - Support DT and ACPI fwnodes
>>      - Put PWM into manual mode
>>      Changes in v3:
>>      - Use the pwm provider/consumer bindings
>>      Changes in v2:
>>      - Use correct device property string for frequency
>>      - Allow -EINVAL and only warn on error
>>      - Use a frequency of 0 to indicate that the hardware should be 
>> left as-is
>>
>>   drivers/hwmon/adt7475.c | 130 ++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 130 insertions(+)
>>
>> diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
>> index 4224ffb30483..fc5605d34f36 100644
>> --- a/drivers/hwmon/adt7475.c
>> +++ b/drivers/hwmon/adt7475.c
>> @@ -21,6 +21,8 @@
>>   #include <linux/of.h>
>>   #include <linux/util_macros.h>
>>   +#include <dt-bindings/pwm/pwm.h>
>> +
>>   /* Indexes for the sysfs hooks */
>>     #define INPUT        0
>> @@ -1662,6 +1664,130 @@ static int adt7475_set_pwm_polarity(struct 
>> i2c_client *client)
>>       return 0;
>>   }
>>   +struct adt7475_pwm_config {
>> +    int index;
>> +    int freq;
>> +    int flags;
>> +    int duty;
>> +};
>> +
>> +static int _adt7475_pwm_properties_parse_args(u32 args[4], struct 
>> adt7475_pwm_config *cfg)
>> +{
>> +    unsigned long freq_hz;
>> +    unsigned long duty;
>> +
>> +    if (args[1] == 0)
>> +        return -EINVAL;
>> +
>> +    freq_hz = 1000000000UL;
>> +    do_div(freq_hz, args[1]);
>> +    duty = 255 * args[3];
>> +    do_div(duty, args[1]);
>> +
>
> Gues I am a bit at loss here, just as 0-day. Why use do_div ? It is 
> only needed
> for 64-bit divide operations.

Mainly because of Uwe's comment on v5. I think I've avoided the original 
u64 issue now that I'm converting fwnode_reference_args::args to a u32 
array. I can probably get away with plain division, although 255 * 
args[3] / args[1] might overflow in theory but shouldn't in practice.

I'll let the earth turn and send out a v7 that uses plain division 
unless someone has a strong opinion that I should sprinkle some more 
u64s around.

>
> Thanks,
> Guenter
>