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. -- Patrick Williams
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