On Tue, Apr 5, 2016 at 12:18 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > On Mon, Apr 4, 2016 at 9:34 PM, Octavian Purdila > <octavian.purdila@xxxxxxxxx> wrote: >> On Mon, Apr 4, 2016 at 7:03 PM, Mark Brown <broonie@xxxxxxxxxx> wrote: >>> On Mon, Apr 04, 2016 at 01:25:56PM +0300, Octavian Purdila wrote: >>>> On Sat, Apr 2, 2016 at 7:24 PM, Mark Brown <broonie@xxxxxxxxxx> wrote: >>> >>>> > What I don't understand is why the flow on inital probe isn't simply to >>>> > register the controller which then triggers the walk of the children. >>>> > That way any bus that supports initial probe also supports hotplug >>>> > without needing to go and manually add a second code path. >>> >>>> Do you mean register the notifier per controller instead of per >>>> subsystem? Either way we need changes at the subsystem level and I >>>> choose to follow the device tree implementation for consistency. >>> >>> No! I mean use the exact same callback you've got now for everything. >>> >>>> The other reason is that (pending other ACPICA changes) we can add >>>> other notification events in the future such as node added or removed >>>> (just like device tree), and in that case the probe and hotplug >>>> handling would be different (and a bit more efficient). >>> >>> Why is probe different to hotplug? We don't need to do that in the >>> normal driver model. >> >> There might be some confusion with the term, I am referring to slave >> hotplug, not controller hotplug. >> >> The way I see it, there are two logical operations: probe of a >> controller and the associated enumeration of the SPI slaves for that >> bus and "hotplug" of new SPI slaves and the enumeration of those >> particular slaves. >> >> When we probe the controller we search DT/ACPI and enumerate all the >> slaves for *that* controller. >> >> When a slave hotplug happens for device tree we get a device node >> notification and we can instantiate the SPI slave based on that info. >> In case of ACPI, (at this point) we get a global callback and in that >> callback we need to iterate through *all* controllers. > > Is that really necessary? > > The namespace rescan could notify the parent of a new node in > acpi_default_enumeration(), couldn't it? We could do that, with some complexity, but I am not sure if it is worth it - see below. And in either case I still don't see how we can avoid two enumeration paths: one from the probe of the controller -> spi_register_master() -> acpi_register_spi_devices() and one from the notification handler -> acpi_register_spi_devices(). Both will end up are calling the same enumeration function but there are still two paths. Even right now, in the case of dynamic DT, we have the two enumeration paths. If we really want to have a single path for ACPI enumeration we could do that by using an ACPI SPI bridge driver or scan handlers after extending the matching mechanisms. But we would still need to modify the SPI subsystem and I don't think its worth it just to save a call to acpi_register_spi_devices() from spi_register_master(). Now for parent notification complexity: in the case of SPI we can easily to this because current ACPI SPI enumeration supports only direct children as slaves. However, on I2C we can have an unrelated node as a slave - that is why the I2C scanning searches the whole namespaces for references to a particular i2c_adapter. So, we would need to retrieve the parent node from the namespace node information which means that we will do SPI specific stuff in ACPI generic code. I don't think it is a big issue, because we already treat SPI / I2C special, right? Once we have the parent handle we would still have to iterate through all controllers to get the spi_master matching the ACPI handle. It is a bit more efficient then global notification, but probably won't matter in practice. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
