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From: Ed Tanous <edtanous@google.com>
Date: Thu, 18 Mar 2021 09:10:38 -0700
Message-ID: <CAH2-KxAva6Sz6Q7GN-B8Tat+K855M1LZ2FiTcqxx7Smui=MqNA@mail.gmail.com>
Subject: Re: Negative value returns for sensor in tiogapass
To: "Ren, Zhikui" <zhikui.ren@intel.com>
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 Jayashree D <jayashree-d@hcl.com>
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On Wed, Mar 17, 2021 at 11:18 AM Ren, Zhikui <zhikui.ren@intel.com> wrote:
>
>
>
> -----Original Message-----
> From: openbmc <openbmc-bounces+zhikui.ren=3Dintel.com@lists.ozlabs.org> O=
n Behalf Of Jayashree D
> Sent: Wednesday, March 17, 2021 12:39 AM
> To: Ed Tanous <edtanous@google.com>
> Cc: openbmc@lists.ozlabs.org
> Subject: RE: Negative value returns for sensor in tiogapass
>
> Classification: Public
>
> Hi Ed,
>
> PMBus spec only have read and write format. In the below link, PXE VR use=
s 11 bit format. Also sign extend the 11bit reading so that negatives show =
correctly.
>
> https://github.com/openbmc/dbus-sensors/commit/e4a970d9aea97c7c1a11c63215=
e7d3cda2124e54#diff-135678dd2046935c5dd0be8e5a5a529d33231203149e786d57b15a3=
cc0cc1240
>
>             constexpr const size_t shift =3D 16 - 11; // 11bit into 16bit
>             value <<=3D shift;
>             value >>=3D shift;
>
> Could anyone from the intel team can clarify the need of above logic used=
 in IpmbSensor.
>
> [Ren, Zhikui]  This change was made to allow negative numbers be reported=
 correctly.  This can happen during test. Without the change, 255degree wil=
l be reported and trip threshold event incorrectly.

Can you walk through what your test was?  It's sounding like Jayashree
was seeing incorrect values in a real world application.  Is it
possible we fixed something in a test by breaking something in the
real world?  Can you think of any other reasons why others would be
seeing different behavior?

> Exponent data is not used because it is always 0.
>
> Regards,
> Jayashree
>
> -----Original Message-----
> From: Jayashree D
> Sent: Tuesday, March 9, 2021 4:48 PM
> To: Ed Tanous <ed@tanous.net>
> Cc: Ed Tanous <edtanous@google.com>; openbmc@lists.ozlabs.org
> Subject: RE: Negative value returns for sensor in tiogapass
>
> Classification: Public
>
> Thanks Ed, I'll check it out.
>
> -----Original Message-----
> From: Ed Tanous <ed@tanous.net>
> Sent: Monday, March 8, 2021 9:37 PM
> To: Jayashree D <jayashree-d@hcl.com>
> Cc: Ed Tanous <edtanous@google.com>; openbmc@lists.ozlabs.org
> Subject: Re: Negative value returns for sensor in tiogapass
>
> [CAUTION: This Email is from outside the Organization. Unless you trust t=
he sender, Don't click links or open attachments as it may be a Phishing em=
ail, which can steal your Information and compromise your Computer.]
>
> On Sun, Mar 7, 2021 at 10:17 PM Jayashree D <jayashree-d@hcl.com> wrote:
> >
> > Classification: Public
> >
> > Hi Ed,
> >
> > In the below link, PXE1410CVR and ADM1278HSC are using the same reading=
 format.
> > I am not able to find any information on PXE1410CVR. If there is any sp=
ec available, could you please share it.
> > It will be helpful to analyze both the specs and fix the problem.
>
> I don't have any specs available for those.  I would assume they follow t=
he pmbus spec though, you might start there.
>
> >
> > https://apc01.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fgit=
h
> > ub.com%2Fopenbmc%2Fdbus-sensors%2Fblob%2Fmaster%2Fsrc%2FIpmbSensor.cpp
> > %23L144&amp;data=3D04%7C01%7Cjayashree-d%40hcl.com%7C8676d30f4d3a4dda1e=
0
> > e08d8e24c4957%7C189de737c93a4f5a8b686f4ca9941912%7C0%7C0%7C63750816456
> > 8775248%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLC
> > JBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=3D5lhuUdfI%2BG75C8I1HDAaE=
H
> > VP46%2Bz1r3nJV0ek3CiiR4%3D&amp;reserved=3D0
> >
> > Regards,
> > Jayashree
> >
> >
> > -----Original Message-----
> > From: Ed Tanous <edtanous@google.com>
> > Sent: Friday, February 26, 2021 9:57 PM
> > To: Jayashree D <jayashree-d@hcl.com>
> > Cc: openbmc@lists.ozlabs.org
> > Subject: Re: Negative value returns for sensor in tiogapass
> >
> > [CAUTION: This Email is from outside the Organization. Unless you
> > trust the sender, Don't click links or open attachments as it may be a
> > Phishing email, which can steal your Information and compromise your
> > Computer.]
> >
> > On Fri, Feb 26, 2021 at 12:55 AM Jayashree D <jayashree-d@hcl.com> wrot=
e:
> > >
> > > Classification: Public
> > >
> > > Hi Team,
> > >
> > >
> > >
> > > Recently, I have tested sensors for tiogapass, in which one sensor re=
turns negative value.
> > >
> > > After analysing the code in the dbus-sensors repo, I found the follow=
ing issue.
> > >
> > >
> > >
> > > dbus-sensors/IpmbSensor.cpp at master * openbmc/dbus-sensors
> > > (github.com)
> > >
> > >
> > >
> > > From the above link, We need only below line in the code to process t=
he HSC sensors value for tiogapass.
> > >
> > >
> > >
> > > int16_t value =3D ((data[4] << 8) | data[3]);
> > >
> > >
> > >
> > > Since the below logic is added, the values get shifted and getting ne=
gative values as output.
> > >
> > >
> > >
> > > constexpr const size_t shift =3D 16 - 11; // 11bit into 16bit
> > >
> > > value <<=3D shift;
> > >
> > > value >>=3D shift;
> > >
> > >
> > >
> > > Could you please suggest any idea to resolve this issue.
> >
> > I haven't looked at this in detail, but we should follow whatever the s=
pec says here.  If whomever wrote this originally put in the wrong math (wh=
ich seems likely, given they were implementing 4 types and probably only us=
ing one) then we should just get it fixed and do what the spec says.
> >
> > >
> > >
> > >
> > > Regards,
> > >
> > > Jayashree
> > >
> > >
> > >
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