Winbond 792 source codes for lm_sensor

Huang0 at Winbond.com.tw Huang0 at Winbond.com.tw
Fri Feb 18 03:29:07 CET 2005


Hi Jean, MDS

As to the voltage factor, after a further study to the 792 data sheet
and /etc/sensors.conf, I find that the interface vol_factor in /proc
can really be removed from the 792 driver. The calculation has been
transferred into /etc/sensors.conf, instead of in the 792 driver.

W83792D is a little different from the previous chips in the following
aspects:
(1) It need two registers to calculate in0-in6 measured value,
instead of one register. But as to in7-in8, only one register.
For example:
Vcore A Voltage = (CR[20]*4 + CR[3E]&0x03) * 0.002;
VcoreB Voltage = (CR[21]*4 + CR[3E]&0xC0) * 0.002;
VIN0 Voltage = (CR[22]*4 + CR[3E]&0x30) * 0.004;
VIN1 Voltage = (CR[23]*4 + CR[3E]&0xC0) * 0.004;
VIN2 Voltage = (CR[24]*4 + CR[3F]&0x03) * 0.004;
VIN3 Voltage = (CR[25]*4 + CR[3F]&0x0C) * 0.004;
5VCC Voltage = (CR[26]*4 + CR[3F]&0x30) * 0.006;
5VSB Voltage = CR[B0] * 0.024;
VBAT Voltage = CR[B1] * 0.016;

(2) The voltage factor for limits are different from the
one for measured value, except in7 and in8. Because:
VcoreA Limit Setup
CR[2B/2C] = [Desired Voltage]/0.008;
VcoreB Limint Setup
CR[2D/2E] = [Desired Voltage]/0.008;
VIN0~VIN3 Limit Setup
CR[2F~36] = [Desired Voltage] / 0.016;
5VCC Limit Setup
CR[37/38] = [Desired Voltage] / 0.024;
5VSB Limit Setup
CR[B4/B5] = [Desired Voltage] / 0.024;
VBAT Limit Setup
CR[B6/B7] = [Desired Voltage] / 0.016;

So, in my previous 792 driver, I had to calculate the voltage in
the driver, instead of in /etc/sensors.conf

But now, I find that as to in0-in6, the factors of voltage limit
are the 4 times to the one of measured value.
So my current calculation method is:
/proc/in0-in6 measured value keep such as (CR[20]*4 + CR[3E]&0x03)
/proc/in7-in8 measured value keep such as CR[B0]
/proc/in0-in6 max value keep such as CR[2B]*4
/proc/in7-in8 max value keep such as CR[B4]
And voltage factors for measured value are added into /etc/sensors.conf.

I test it roughtly, it seems to work well. :-)


Best Regards
Chunhao
2005-02-18


> > > - Why is the vol_factor array exposed to /proc? Isn't this only
for
> > >   debugging?
> > >   These shouldn't be exposed to the user. If the user needs to
> > >   adjust computation it can be done in /etc/sensors.conf.
> >
> > In the requirements of our customer: the motherboard vendor should
> > have the permission to modify the voltage factor, so I expose it
into
> > /proc. I write it with the reference of our Windows version, the
> > Windows version GUI supply a interface to modify the voltage factor,
> > but it need authentication, That's to say, NOT all of the user can
> > modify it.
> 
> As I understand it, these factors account for the resistors placed on
> the motherboard, which are needed to bring all voltages back into the
> measurable 0V-4V range. Am I correct?
> 
> Is so, this does indeed not belong to the driver and has to be
removed.
> Such computation has always been performed in userspace by libsensors,
> for all drivers. The reason for this is that libsensors can do almost
> any mathematical operation, not only apply factors. As a matter of
fact,
> the W83792D chip needs more than factors for -5V and -12V (an
additional
> offset is needed), and unless I am missing something, your driver
> doesn't handle that. There is also a kernel development policy which
> states that conversions should always be moved outside of the kernel
> when possible, and this is exactly what libsensors is there for.
> 
> The "authentification" issue you are talking about is unrelated. The
> root user (and only him/her) will possibly change the voltage factors,
> regardless of the method (/proc or libsensors) - not the "motherboard
> vendor".
> 
> As a side note, I'm already not certain that restricting the access to
> these values in the Windows world makes sense, but I am certain that
it
> makes no sense in the Linux world. The goal of open-source tools is to
> give the users the possibility to change whatever them want to, and
> certainly not to put restrictions to what they are allowed to do. And
at
> any rate there is no room for such a restriction mechanism in the
> libsensors framework.
> 
> As a side note, the voltage factors were used in your driver for the
> measured values only, not for the limits (unless I missed something)
so
> it was not working correctly anyway.


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