Re: [lm-sensors] [PATCH] hwmon class driver registration with adevice number

From: Alan Cox
Date: Thu Oct 06 2011 - 11:48:38 EST

> AFAIK, the current sysfs interface is to read standard attributes from
> the device. My reasoning is:

and any other attributes.

> 1. This will give hwmon devices to have their "dev" in their sysfs folder
> as like other classes and in turn be visible in /dev by mdev or udev.

Well there is in theory no reason a device shouldn't do that, but most
sysfs devices don't need to so making it generic seems odd.

> 2. Implementing IOCTL if required. I know that kernel hackers believe
> they are "backdoors" and "can't be done right" but sometimes there
> isn't any get away with them. I don't know when their support will
> be completely removed. Rather, I see that instead of deprecation,
> new IOCTL vectors like compat_ioctl have been introduced.

Certain things need ioctl, in fact some problems are *very* hard to
solve any other way: transactional updates (changing a set of fields at
once all or none), and query/response data being two.

> 2. During probing, for each device, call "hwmon_device_register_numbered"
> and let mdev create a /dev node for it. I don't say that this interface
> be imposed on drivers. If they want they can still call "hwmon_device_register"
> if they don't want to implement standard ioctl, read, write calls.

I guess I don't see why a device that is more than just a monitoring
interface can't allocate a misc device or similar if it needs one.

For the more complex cases take a look at drivers/staging/iio also.
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