Re: [PATCH] [RFC] hwmon: nct6775: Register fan PWMs as PWM chip

[Richard Weinberger <richard@nod.at>]

Hello Guenter,

----- Ursprüngliche Mail -----
> Von: "Guenter Roeck" <linux@roeck-us.net>
>>   - Exporting a PWM for external use is only allowed when the fan mode
>>     is set to manual or off.
>>   - As soon as a PWM is exported, changing its configuration is no
>>     longer possible through the hwmon sysfs interface, reading is
>>     still allowed.
>>   - Changing the PWM period is not supported. IMHO, it is too risky
>>     since the PWMs usually control system fans and similar components.
>>   - Reading and decoding the current PWM period is only supported for
>>     one chip variant so far, for all other chips, a fixed period of
>>     100ms is assumed.
>> 
> 
> This is a good start, but I'll want to see stronger safeguards.
> - Creating a pwmchip entry for a pwm channel must be triggered by
>   device property data, obtained either from devicetree or through
>   DMI or through device properties embedded in ACPI data. For each
>   channel, this must be confirmed by checking that the channel is
>   not associated with a fan control channel.

In my case it's a x86 based industrial PC with direct access.
What safeguard do you suggest in this case? A module parameter?

Also for ACPI data, what exactly do you have in mind?

> - If a pwm channel is configured as pwmchip, it must not be used for fan
>   control, meaning the hwmon properties associated with that channel
>   must not be created.

Ok.
 
> This will retain current functionality while enabling support for using
> pwm channels for purposes other than fan control.
> 
> Thanks,
> Guenter