On 2022/11/3, 1:01 AM, "Guenter Roeck" <groeck7@xxxxxxxxx on behalf of linux@xxxxxxxxxxxx> wrote:
On Wed, Nov 02, 2022 at 06:54:43AM +0000, Billy Tsai wrote:
> > Hi Guenter,
> >
> > On 2022/11/1, 9:15 PM, "Guenter Roeck" <groeck7@xxxxxxxxx on behalf of linux@xxxxxxxxxxxx> wrote:
> >
> > On Tue, Nov 01, 2022 at 05:51:56PM +0800, Billy Tsai wrote:
> > > > +
> > > > + /* Restart the Tach channel to guarantee the value is fresh */
> > > > + aspeed_tach_ch_enable(priv, fan_tach_ch, false);
> > > > + aspeed_tach_ch_enable(priv, fan_tach_ch, true);
> >
> > > Is that really needed ? Doesn't the controller measure values continuously ?
> >
> > Yes, the controller will measure values continuously by hardware. I will remove it.
> > If the user want to get the fresh value, it should be done by the application layer
> > (e.g. read two times).
> >
> > > > +
> > > > + if (ret) {
> > > > + /* return 0 if we didn't get an answer because of timeout*/
> > > > + if (ret == -ETIMEDOUT)
> > > > + return 0;
> > > > + else
> > > > + return ret;
> >
> > > else after return is unnecessary, and why would a timeout be be ignored ?
> >
> > When the user sets the correct fan information (i.e., min_rpm, max_rpm), the read
> > poll timeout will only occur if the tach pin does not get any signal (i.e. rpm=0).
> >
> In that case it would be appropriate to return -ETIMEDOUT to the caller.
> Anyway, that should really not happen. Sysfs attributes such as minimum/maximum fan
> speed, the number of fan pulses per revolution, or a divider value should only exist
> if the chip needs that information, for example to report a fan error/alarm if the
> measured speed is out of range or if the chip actually calculates RPM and provides
> the result to the driver. Those values should not be necessary (and should not be
> used) to calculate some timeout.
Can't I use a min/max RPM to let the driver know a reasonable timeout/polling period when
the driver is trying to get RPM?
Beacause that our tach controller have the falg to indicates the hardware detected the change
in the input signal. I need the proper timout to rule out slow RPMs.
Thanks
Best Regards,
Billy Tsai
