Peter Maydell <peter.mayd...@linaro.org> writes: > On 18 October 2016 at 21:49, Eduardo Habkost <ehabk...@redhat.com> wrote: >> On Tue, Oct 18, 2016 at 09:30:01PM +0100, Peter Maydell wrote: >>> Lots of stuff in a device's C struct is strictly internal >>> and not to be messed with. I thought that QOM properties >>> were essentially how a device defined its public (and >>> typically settable-only-once) config knobs. QOM properties >>> shouldn't be user-facing (read: stable, required to be >>> backwards-compatible) interface in general because >>> we don't really want to tie ourselves down that much. >>> In fact almost all our QOM objects are not usefully >>> user-facing at all. >> >> This interpretation surprises me, because it is the opposite of >> what I have seen us doing. Most of our QOM objects and properties >> are user-visible and user-configurable using -global, -device, >> -object, or qom-set (and probably other QMP commands). > > Most of the devices I deal with are not and never will > be sensibly usable with -device. Exposing wiring up > of IRQ and GPIO lines or MMIO regions to the user is > never going to make sense. For x86 most devices are > probably pluggable (and usable with -device), but over > the whole source tree I think the embedded-style device > is in the majority. They're all still worth QOMifying > and having properties for the things board code wants > to modify, though.
"Device not pluggable" does not imply "device has no configuration knobs a user may legitimately want to mess with". Plenty of onboard devices have such knobs. Right now, users configure these mostly via board-agnostic options like -serial. Anything that doesn't fit the mold can't be configured that way. However, A fully mature QOM as I envisage it would provide users access to QOM properties for onboard devices, too. Not with -device, obviously, but with qom-set and similar, as Eduardo said. If any of these properties are not for users, they should be marked as such. Just like for pluggable devices. Perhaps non-pluggable devices tend to have more "not for users" QOM properties than pluggable ones, I don't know. But that would be a *quantitative* difference, not a *qualitative* one.
