On Fri, Oct 22, 2021 at 10:18:11AM -0500, Patrick Williams wrote: > Hi Greg, > > On Fri, Oct 22, 2021 at 10:57:21AM +0200, Greg Kroah-Hartman wrote: > > On Fri, Oct 22, 2021 at 01:32:32AM -0700, Zev Weiss wrote: > > > On Thu, Oct 21, 2021 at 11:46:56PM PDT, Greg Kroah-Hartman wrote: > > > > On Thu, Oct 21, 2021 at 07:00:31PM -0700, Zev Weiss wrote: > > > > So we want the kernel to be aware of the device's existence (so that we > > > *can* bind a driver to it when needed), but we don't want it touching the > > > device unless we really ask for it. > > > > > > Does that help clarify the motivation for wanting this functionality? > > > > Sure, then just do this type of thing in the driver itself. Do not have > > any matching "ids" for this hardware it so that the bus will never call > > the probe function for this hardware _until_ a manual write happens to > > the driver's "bind" sysfs file. > > It sounds like you're suggesting a change to one particular driver to satisfy > this one particular case (and maybe I'm just not understanding your suggestion). > For a BMC, this is a pretty regular situation and not just as one-off as Zev's > example. > > Another good example is where a system can have optional riser cards with a > whole tree of devices that might be on that riser card (and there might be > different variants of a riser card that could go in the same slot). Usually > there is an EEPROM of some sort at a well-known address that can be parsed to > identify which kind of riser card it is and then the appropriate sub-devices can > be enumerated. That EEPROM parsing is something that is currently done in > userspace due to the complexity and often vendor-specific nature of it. > > Many of these devices require quite a bit more configuration information than > can be passed along a `bind` call. I believe it has been suggested previously > that this riser-card scenario could also be solved with dynamic loading of DT > snippets, but that support seems simple pretty far from being merged. Then work to get the DT code merged! Do not try to create yet-another-way of doing things here if DT overlays is the correct solution here (and it seems like it is.) thanks, greg k-h
