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

[Alex Qiu]

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...

- 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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