Dealing with a sensor which doesn't have valid reading until host is powered up

[Alex Qiu]

Hi Guenter,

For that, this was referring to the OpenBMC application. What I meant is
that even normal sensors stopped working... . Sry for the confusion...

- Alex Qiu


On Thu, Sep 3, 2020 at 8:31 AM Guenter Roeck <groeck at google.com> wrote:

> On Wed, Sep 2, 2020 at 3:07 PM Alex Qiu <xqiu at google.com> wrote:
> >
> > Hi James,
> >
> > I just tried, now I have no reading at all... I saw you marked your pull
> request to work in progress. I'll wait for further updates...
> >
> I may be missing something, but isn't that the idea ?
>
> Thanks,
> Guenter
>
> > - Alex Qiu
> >
> >
> > On Wed, Sep 2, 2020 at 1:31 PM Alex Qiu <xqiu at google.com> wrote:
> >>
> >> Hi James,
> >>
> >> I think Ed has mentioned the same thing in an internal discussion. I'll
> give it a try.
> >>
> >> Anyhow, as discussed with Guenter, EAGAIN still may not be a good use
> of our case here, as it's not something that a busy loop should wait for.
> I've also changed the driver to return ENODATA.
> >>
> >> Thanks!
> >>
> >> - Alex Qiu
> >>
> >>
> >> On Wed, Sep 2, 2020 at 10:59 AM James Feist <
> james.feist at linux.intel.com> wrote:
> >>>
> >>> On 8/31/2020 3:08 PM, Alex Qiu wrote:
> >>> > Hi James,
> >>> >
> >>> > I just came through this doc
> >>> > (
> https://www.boost.org/doc/libs/1_74_0/doc/html/boost_asio/overview/posix/stream_descriptor.html
> ).
> >>> > Looks like that it's a terrible idea for hwmon driver to return
> EAGAIN
> >>> > for dbus-sensors. With that, I think the proper fix is also to use
> other
> >>> > errno instead in our driver, and this caveat should be probably
> >>> > documented somewhere.
> >>> >
> >>>
> >>> Hi Alex,
> >>>
> >>> I hit something similar with peci where timeouts was causing the scan
> >>> loop to hang. I remembered that back when we were developing ipmbbridge
> >>> we hit something similar with i2c, and the work around was to use the
> >>> tcp socket instead
> >>>
> https://www.boost.org/doc/libs/1_74_0/doc/html/boost_asio/reference/ip__tcp/socket.html
> >>> as it could correctly handle the errors. This worked for me for the
> >>> CpuSensor and is a easy to implement change that might be worth trying
> >>> for other sensors
> >>> https://gerrit.openbmc-project.xyz/c/openbmc/dbus-sensors/+/36181.
> >>>
> >>> Thanks
> >>>
> >>> James
>
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