Re: [PATCH v2 1/2] dt-bindings: Add power-efuse binding

[Rob Herring <robh@kernel.org>]

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@bewilderbeest.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@bewilderbeest.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--->????

Rob