Re: Enabling pmbus power control

[Zev Weiss]

On Tue, Apr 20, 2021 at 12:15:40PM CDT, Mark Brown wrote:
> On Tue, Apr 20, 2021 at 11:40:24AM -0500, Zev Weiss wrote:
> > On Tue, Apr 20, 2021 at 11:13:18AM CDT, Mark Brown wrote:
>
> > > I already suggested writing a driver or drivers that represent the
> > > hardware you have, that advice remains.  It's hard to follow what you
> > > were trying to say with your long mail earlier today but it seems like
>
> > That email was an attempt to explain why writing a driver for the specific
> > hardware devices we're powering seems like a poor fit to me.  To summarize:
>
> >  - There's a wide variety of different devices potentially behind an
> > LM25066.
>
> This is true for lots of hardware, we still integrate things into
> frameworks.
>
> >  - A hypothetical driver for any one of them would be completely
> > non-specific to that device and functionally identical to a driver    for
> > any other, because the only hardware it would actually be    touching is the
> > LM25066, and in ways that are again completely    non-specific to anything
> > but the LM25066 itself.
>
> I don't see why that would be the case at all.  Even within the indended
> application as a power controller for a hotpluggable bus there's plenty
> of potential for integration into a wider representation of the socket
> things get inserted into - for example I've worked with buses that had
> support for operator signalling of hotplug (buttons to press to initiate
> hot removal, with lights to signal when a clean shutdown of the card had
> been completed), you might also want to have additional environment
> monitoring and of course the labelling that I mentioned in an earlier
> post.  I can imagine you probably have some other connection of some
> kind to the host too (eg, network ports) to join up and perhaps sync
> hotplug for.

Consider the power shelf I mentioned earlier -- it's a rackmount power 
supply and that's about it.  It provides DC power to arbitrary devices 
that it has no other connection to, just ground and +12V.  Those devices 
might be servers, or cooling fans, or vacuum cleaners or floodlights -- 
the power shelf doesn't know, or care.  It's a lot like a switchable 
network PDU in that it just provides a way for an operator to remotely 
cut power to a thing that's plugged into it.  There's no other bus or 
anything in the picture.  (And pragmatically, given that its most common 
usage is likely to be to provide a cold power cycle as a last-ditch 
recovery option when things are wedged in some unresponsive state, 
attempting any sort of coordination with the downstream device would 
probably be a dead end anyway.)


Zev