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From: Mike Jones <proclivis@gmail.com>
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Subject: Re: No dbus objects for phosphor-regulators
Date: Fri, 11 Feb 2022 15:56:18 -0700
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To: Ed Tanous <edtanous@google.com>
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> On Feb 11, 2022, at 1:20 PM, Ed Tanous <edtanous@google.com> wrote:
>=20
> =EF=BB=BFOn Fri, Feb 11, 2022 at 8:06 AM Shawn McCarney <shawnmm@linux.ibm=
.com> wrote:
>>=20
>> On 2/11/2022 9:42 AM, Mike Jones wrote:
>>=20
>> I was mainly surprised because a conversation I had with Guenter, if I re=
member correctly, suggested that /dev/i2c calls from user space work with hw=
mon, because hwmon does not lock the i2c except when using it.
>>=20
>> So I assumed that in this case, it was the polling of hwmon that was just=
 keeping it locked enough to conflict with phosphor-regulators and then it g=
ives up.
>>=20
>> With i2c-dev, you can specify I2C_SLAVE or I2C_SLAVE_FORCE when creating t=
he connection.  I believe I2C_SLAVE will cause communication attempts to fai=
l if a driver is bound.  I2C_SLAVE_FORCE will still try to communicate.
>>=20
>> I wanted to take the more conservative approach, because there are scenar=
ios where interleaving communication can cause serious problems.  For exampl=
e, if one PMBus regulator supports multiple rails, you have to set the PMBus=
 PAGE register to the rail you are interested in.  Subsequent PMBus commands=
 will affect that rail.  If phosphor-regulators and a driver are both commun=
icating with the regulator, they may both be setting PAGE and thus their sub=
sequent commands are going to the wrong rail.
>>=20
>>=20
>> I could just not use hwmon at all use phosphor-regulators for all telemet=
ry, but this seemed like more work.
>>=20
>> Sorry about that.  I think if you have already done the work of defining t=
he regulator and a read sensors rule in your JSON file, adding a few more se=
nsors is not much additional work though.  Let me know if you have questions=
.
>>=20
>> Also, I will need to figure out how to connect phosphor-regulators teleme=
try to Redfish and the WebUI. Are there examples of how to do that?
>>=20
>> It should just work with no additional effort as long as you define the f=
ollowing correctly in your JSON file:
>>=20
>> * The "inventory_path" property of your "chassis" object needs to match a=
 real chassis inventory item on D-Bus.
>>=20
>> * The "fru" property of your regulator "device" object needs to match a r=
eal inventory item on D-Bus.  As I mentioned earlier, normally if the regula=
tor is pluggable then this is the regulator itself.  Otherwise it is the lar=
ger hardware item that contains it, such as a motherboard.  FRU is the acron=
ym for Field Replaceable Unit, referring to a pluggable hardware item.
>>=20
>> phosphor-regulators will publish your sensors on D-Bus with the standard o=
bject paths and properties.  The two JSON properties above are used to defin=
e a "chassis" association and an "inventory_item" association on D-Bus that i=
s used by bmcweb.  This will cause your sensors to appear in Redfish and the=
 Web UI.
>>=20
>> Thanks,
>>=20
>> Shawn
>=20
> This same topic is essentially being discussed in a design doc here:
> https://gerrit.openbmc-project.xyz/c/openbmc/docs/+/50509

I will move my discussion to Gerrit.

Note that I work for ADI, my team supports ADM1266, ADM1278, LTC297X, LTC388=
X, the MAX devices in this category, and I am on the SMIF (PMBus) Board and o=
n the PMBus Technical Committee.

>=20
> I've CCed the relevant parties from that review on this thread, and I
> don't have a strong opinion what forum we use to discuss this, but we
> should ideally all be talking together on a common solution.