RE: Negative value returns for sensor in tiogapass

[Jayashree D <jayashree-d@hcl.com>]

Classification: Public

Hi Ed,

PMBus spec only have read and write format. In the below link, PXE VR uses 11 bit format. Also sign extend the 11bit
reading so that negatives show correctly.

https://github.com/openbmc/dbus-sensors/commit/e4a970d9aea97c7c1a11c63215e7d3cda2124e54#diff-135678dd2046935c5dd0be8e5a5a529d33231203149e786d57b15a3cc0cc1240

            constexpr const size_t shift = 16 - 11; // 11bit into 16bit
            value <<= shift;
            value >>= shift;

Could anyone from the intel team can clarify the need of above logic used in IpmbSensor.

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

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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 spec 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 the pmbus spec though, you might start there.

>
> https://apc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgith
> ub.com%2Fopenbmc%2Fdbus-sensors%2Fblob%2Fmaster%2Fsrc%2FIpmbSensor.cpp
> %23L144&amp;data=04%7C01%7Cjayashree-d%40hcl.com%7C8676d30f4d3a4dda1e0
> e08d8e24c4957%7C189de737c93a4f5a8b686f4ca9941912%7C0%7C0%7C63750816456
> 8775248%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLC
> JBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=5lhuUdfI%2BG75C8I1HDAaEH
> VP46%2Bz1r3nJV0ek3CiiR4%3D&amp;reserved=0
>
> 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> wrote:
> >
> > Classification: Public
> >
> > Hi Team,
> >
> >
> >
> > Recently, I have tested sensors for tiogapass, in which one sensor returns negative value.
> >
> > After analysing the code in the dbus-sensors repo, I found the following 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 the HSC sensors value for tiogapass.
> >
> >
> >
> > int16_t value = ((data[4] << 8) | data[3]);
> >
> >
> >
> > Since the below logic is added, the values get shifted and getting negative values as output.
> >
> >
> >
> > constexpr const size_t shift = 16 - 11; // 11bit into 16bit
> >
> > value <<= shift;
> >
> > value >>= 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 spec says here.  If whomever wrote this originally put in the wrong math (which seems likely, given they were implementing 4 types and probably only using one) then we should just get it fixed and do what the spec says.
>
> >
> >
> >
> > Regards,
> >
> > Jayashree
> >
> >
> >
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