Message-ID: <YivrqQA4r2hQ+xSL@hatter.bewilderbeest.net>
Date:   Fri, 11 Mar 2022 16:39:05 -0800
From:   Zev Weiss <zev@...ilderbeest.net>
To:     Rob Herring <robh@...nel.org>
Cc:     devicetree@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        openbmc@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v2 1/2] dt-bindings: Add power-efuse binding

On Fri, Mar 11, 2022 at 04:08:47PM PST, Rob Herring wrote:
>On Fri, Mar 11, 2022 at 01:48:22PM -0800, Zev Weiss wrote:
>> On Fri, Mar 11, 2022 at 07:24:41AM PST, Rob Herring wrote:
>> > On Mon, Mar 07, 2022 at 05:18:09PM -0800, Zev Weiss wrote:
>> > > This can be used to describe a power output supplied by a regulator
>> > > device that the system controls.
>> > >
>> > > Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
>> > > ---
>> > >  .../devicetree/bindings/misc/power-efuse.yaml | 49 +++++++++++++++++++
>> > >  1 file changed, 49 insertions(+)
>> > >  create mode 100644 Documentation/devicetree/bindings/misc/power-efuse.yaml
>> > >
>> > > diff --git a/Documentation/devicetree/bindings/misc/power-efuse.yaml b/Documentation/devicetree/bindings/misc/power-efuse.yaml
>> > > new file mode 100644
>> > > index 000000000000..5f8f0b21af0e
>> > > --- /dev/null
>> > > +++ b/Documentation/devicetree/bindings/misc/power-efuse.yaml
>> > > @@ -0,0 +1,49 @@
>> > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>> > > +%YAML 1.2
>> > > +---
>> > > +$id: http://devicetree.org/schemas/misc/power-efuse.yaml#
>> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> > > +
>> > > +title: Generic power efuse device
>> > > +
>> > > +maintainers:
>> > > +  - Zev Weiss <zev@...ilderbeest.net>
>> > > +
>> > > +description: |
>> > > +  This binding describes a physical power output supplied by a
>> > > +  regulator providing efuse functionality (manual on/off control, and
>> > > +  auto-shutoff if current, voltage, or thermal limits are exceeded).
>> > > +
>> > > +  These may be found on systems such as "smart" network PDUs, and
>> > > +  typically supply power to devices entirely separate from the system
>> > > +  described by the device-tree by way of an external connector such as
>> > > +  an Open19 power cable:
>> > > +
>> > > +  https://www.open19.org/marketplace/coolpower-cable-assembly-8ru/
>> >
>> > Not really a helpful link...
>> >
>> > I still don't understand what the h/w looks like here. At least I now
>> > understand we're talking a fuse on power rail, not efuses in an SoC
>> > used as OTP bits or feature disables.
>> >
>>
>> The systems this would actually be used for would be things like these:
>>  - https://www.open19.org/marketplace/delta-16kw-power-shelf/
>>  - https://www.open19.org/marketplace/inspur-open19-power-shelf-ob19200l1/
>
>Those still don't help show me what the h/w looks like. High level
>schematics is what I'm looking for.
>
>
>> The rightmost pictures on those pages show the four black connectors where
>> the cable assembly linked in the patch plugs in, each of which provides the
>> outputs from 12 such efuses, on 12 pairs of ground and +12VDC pins.  (There
>> are also two more single outputs off to the side.)
>>
>> It essentially just amounts to an external power output supplied by a
>> regulator, with the regulator providing an on/off switch, overcurrent
>> protection, etc.
>>
>> And yes, the ambiguity of the "efuse" terminology is unfortunate (the
>> "power-" prefix was an attempt to clarify it slightly).  That's the term
>> used in the documentation for the hardware and hence is what I've called it
>> here, but I'd be open to using a different name if that would help.
>>
>> > > +
>> > > +properties:
>> > > +  compatible:
>> > > +    const: power-efuse
>> > > +
>> > > +  vout-supply:
>> > > +    description:
>> > > +      phandle to the regulator providing power for the efuse
>> >
>> > Vout is a supply to the efuse and not the rail being fused?
>>
>> Yeah, that was a fairly muddled description -- it's really the latter.
>> Perhaps:
>>
>>   phandle to the regulator providing power for the output rail
>>   controlled by the efuse
>>
>> ?
>>
>> >
>> > Sorry, I know nothing about how an efuse is implemented so you are going
>> > to have to explain or draw it.
>> >
>> > > +
>> > > +  error-flags-cache-ttl-ms:
>> > > +    description:
>> > > +      The number of milliseconds the vout-supply regulator's error
>> > > +      flags should be cached before re-fetching them.
>> >
>> > How does one fetch/read? the error flags?
>> >
>>
>> In the specific case I'm dealing with, via PMBus STATUS_* commands, though I
>> was aiming to keep this more generic so it could potentially be used to
>> describe non-PMBus arrangements (in the Linux case, via whatever mechanism
>> the implementation of the regulator's .get_error_flags() function uses).
>
>PMBus is I2C (subset). What device(s) is on the PMBus?
>
>Here's what I've got for connections so far:
>
>Vout(regulator)-->|efuse|-->12V
>
>Host-->PMbus--->????
>

On the hardware I'm currently working with (the Delta unit linked 
above), the PMBus device is a TI LM25066 with various other components 
(MOSFET, thermal diode, sense resistor, etc.) in the surrounding 
circuitry.  My understanding is that "efuse" as used by the manufacturer 
refers to the combined circuit, including the LM25066.

Is that a sufficient "high level schematic", or is there additional 
information you're looking for?  I do have access to a detailed 
schematic of the circuit, but unfortunately I don't think I'm at liberty 
to share it.

(I don't know exactly what the Inspur unit uses because I haven't dealt 
with that one first-hand, but I'd guess it's probably broadly similar.)


Thanks,
Zev

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