[Nouveau] [lm-sensors] hwmon API update

[Lucas Stach]

Am Donnerstag, den 03.03.2011, 18:29 +0100 schrieb Martin Peres:
> Le 03/03/2011 16:22, Guenter Roeck a écrit :
> > On Thu, Mar 03, 2011 at 04:36:09AM -0500, Dave Airlie wrote:
> >> On Mon, Feb 14, 2011 at 8:08 AM, Jean Delvare<khali at linux-fr.org>  wrote:
> >>> On Sun, 13 Feb 2011 09:16:40 -0800, Guenter Roeck wrote:
> >>>> On Sun, Feb 13, 2011 at 07:18:44AM -0500, Martin Peres wrote:
> >>>>> Hi,
> >>>>>
> >>>>> I am working on power management on the nouveau driver and I need a way
> >>>>> to get data out of and send commands to the i2c drivers from the kernel
> >>>>> space.
> >> Martin,
> >>
> >> you probably should have cc'ed Matthew since it was his patch you based this on,
> >> and I think he can provide a good explaination.
> >>
> >> to clarify some points,
> >>
> >> radeon does probably want something exactly like this, we just haven't gotten to
> >> it completely yet, I'd rather not have two drivers in the kernel for
> >> exact same hardware,
> >> and I believe sharing the hwmon code to do what we want is a good plan since you
> >> don't go around reinventing wheels, but if hwmon/i2c maintainers have
> >> no interest
> >> it leaves with little choice but to implement about 5-10 i2c drivers
> >> again in drm codebase.
> >>
> >> Maybe hwmon/i2c maintainers could suggest a cleaner way to implement
> >> what we want,
> >> which I think I can summarize as
> >>
> >> a) access to monitored values in-kernel
> >> b) no userspace access to the same values except via sanitised via the driver.
> >>
> > This is not a matter of "no interest". Interest is there, but if one demands
> > too much one may get nothing.
> >
> > Request for b) so far was "no userspace access", period. This is unacceptable
> > since providing userspace access to monitored values is the whole point of hwmon.

And that is what we want to do. But it would be nice if the graphics
drivers could provide a _single_ interface to userspace. Not all boards
have i2c hardware monitoring chips and with a single interface we could
fall back to the internal gpu sensor, transparently for the user.

> >
> > I could imagine an API that covers both a) and b), as long as b) focuses
> > on the "sanitize" aspect and doesn't try to limit userspace access to attributes.
> >
> > Guenter
> b) was introduced by Dave, I never asked for it because I don't mind 
> duplicating sensor data (one hwmon device named nouveau and one for the 
> raw access to the i2c chip).

Sorry for the confusion Martin, I brought up the point of limiting
userspace access and did not cc the nouveau mailing list. I think it is
bad behaviour to expose values to userspace which are totally off the
real values. This confuses users and should be avoided, especially since
we can provide sanitized values.

Why should we push the logic and api for sanitizing the values to many
hwmon drivers if we could easily do this at a single point in the
graphics driver, if we provide the userspace interface ourself and use
the hwmon driver only to instrument the monitoring chip?

> My only wish was to provide a simple way for users to read/change their 
> fan speed and get the GPU temperature no matter if their card have an 
> i2c controller or not.
> I do agree that sanitizing could be of interest, I especially think 
> about tweaking the temperature value with parameters stored inside the 
> vbios.
> 
> I am fully open to suggestions as long as it involves sharing the code 
> in one way or another.
> 
> Martin
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