On Mon, Apr 19, 2021 at 08:29:53PM -0500, Zev Weiss wrote: > On Tue, Mar 30, 2021 at 02:38:10PM CDT, Guenter Roeck wrote: > > On Tue, Mar 30, 2021 at 07:02:00PM +0100, Mark Brown wrote: > > > On Tue, Mar 30, 2021 at 12:56:56PM -0500, Zev Weiss wrote: > > > > > > > Okay, to expand a bit on the description in my initial message -- we've > > > > got a single chassis with multiple server boards and a single manager board > > > > that handles, among other things, power control for the servers. > > > > The manager board has one LM25066 for each attached server, which acts as > > > > the "power switch" for that server. There thus really isn't any driver to > > > > speak of for the downstream device. > > > > > > This sounds like you need a driver representing those server boards (or > > > the slots they plug into perhaps) that represents everything about those > > > boards to userspace, including power switching. I don't see why you > > > wouldn't have a driver for that - it's a thing that physically exists > > > and clearly has some software control, and you'd presumably also expect > > > to represent some labelling about the slot as well. > > > > Absolutely agree. > > > > Thanks, > > Guenter > > Hi Guenter, Mark, > > I wanted to return to this to try to explain why structuring the kernel > support for this in a way that's specific to the device behind the PMIC > seems like an awkward fit to me, and ultimately kind of artificial. > > In the system I described, the manager board with the LM25066 devices is its > own little self-contained BMC system running its own Linux kernel (though > "BMC" is perhaps a slightly misleading term because there's no host system > that it manages). The PMICs are really the only relevant connection it has > to the servers it controls power for -- they have their own dedicated local > BMCs on board as well doing all the usual BMC tasks. A hypothetical > dedicated driver for this on the manager board wouldn't have any other > hardware to touch aside from the pmbus interface of the LM25066 itself, so > calling it a server board driver seems pretty arbitrary -- and in fact the > same system also has another LM25066 that controls the power supply to the > chassis cooling fans (a totally different downstream device, but one that > would be equally well-served by the same software). > > More recently, another system has entered the picture for us that might > illustrate it more starkly -- the Delta Open19 power shelf [0] supported by > a recent code release from LinkedIn [1]. This is a rackmount power supply All I can see is that this code is a mess. > with fifty outputs, each independently switchable via an LM25066 attached to > an on-board BMC-style management controller (though again, no host system > involved). We (Equinix Metal) are interested in porting a modern OpenBMC to > it to replace the dated, crufty, pre-Linux-Foundation version of OpenBMC it > currently runs (as found in the linked repo). The exact nature of the > devices powered by its outputs is well outside the scope of the firmware > running on that controller (it could be any arbitrary thing that runs on > 12VDC), but we still want to be able to both (a) retrieve per-output > voltage/current/power readings as provided by the existing LM25066 hwmon > support, and (b) control the on/off state of those outputs from userspace. > > Given the array of possible use-cases, an approach of adding power-switch > functionality to the existing LM25066 support seems like the most obvious > way to support this, so I'm hoping to see if I can get some idea of what an > acceptable implementation of that might look like. > Sorry, that is simply a no-go for the LM25066 driver. I mentioned it before, and it is still true: The hwmon subsystem is not in the business of power control. Have you looked into enclosures (drivers/misc/enclosure.c) ? Maybe that or something similar could be used for your purposes. Thanks, Guenter
