[lm-sensors] use of struct platform_device vs struct device in

[jim.cromie@gmail.com (Jim Cromie)]

Jean Delvare wrote:
> Hi Jim,
>
>   
>> while LXR'g  (http://sosdg.org/~coywolf/lxr/)
>> for usage of struct platform_device, I found your code.
>>
>> What were your reasons for using platform_device, what are the benefits ?
>>
>> Were they special-case considerations, or is this something that
>> other hwmon drivers should consider moving towards ?
>>     
>
> Well, the reasons were simply that the Fintek F71805F/FG is not an
> I2C/SMBus device. For too long, all hardware monitoring drivers have
> been implemented as i2c drivers, even when they were absolutely not
> I2C/SMBus related. This was made possible by the i2c-isa driver, which
> has an historical reason for existing: some chips (LM78 and W83781D to
> name the most popular ones) used to have two possible interfaces, I2C
> and ISA. In order to avoid code duplication while keeping the drivers
> simple, it was decided to handle the ISA interface as a fake I2C bus.
>
> Now, there are more and more hardware monitoring devices which are
> either integrated into PCI devices, of integrated into Super-I/O chips,
> with a simple ISA interface. Depending on the whole i2c stack to drive
> these is quite boring and inefficient now, so I have been working on a
> clean separation between i2c and hwmon for the past few months. This
> included a full rewrite of i2c-isa, and moving of all hardware
> monitoring drivers from drivers/i2c/chips to drivers/hwmon, and a lot
> of cleanups all around the place. Then we introduced the hwmon class,
> which makes it possible for user-space to locate hardware monitoring
> chips in sysfs regardless of their interface. This was supported by
> libsensors in lm_sensors 2.9.2 for the first time.
>
> The ultimate goal is to convert all non-I2C hardware monitoring drivers
> to platform drivers. However, we need to wait for lm_sensors 2.9.2 and
> later to be widely deployed before we modify the exiting drivers, as it
> makes them incompatible with earlier releases of lm_sensors. For the
> f71805f driver, it was new so compatibility wasn't an issue. All other
> drivers, except the newly ported vt8231 driver, will have to wait at
> least another 6 months before we can consider converting them. New
> drivers or drivers being ported these days (e.g. vt1211) should be
> implemented as platform drivers directly.
>
> I hope I clarified the point :)
>
>   
Thanks Jean,

A helpful and thorough answer, thanks.
WRT waiting for 2.9.2,  it would take some months to get updates
thru -mm and then into mainline.   Certainly drivers could sit in -mm
until the time is right.


Actually though, the question I posed was twisted from an OT one;
Im working on pc8736x_gpio, which is an adaptation of scx200_gpio,
so its a char-dev.  I was looking for a way to get a struct device that
I could use in dev_dbg() and friends,

I may imitate your work in pc87360, just to get some familiarity
with platform_device, (along with on-topic help ;-), then apply that
to my gpio project.