On Fri, Oct 9, 2020 at 7:27 AM Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com wrote:
- ancildrv->driver.owner = owner;
- ancildrv->driver.bus = &ancillary_bus_type;
- ancildrv->driver.probe = ancillary_probe_driver;
- ancildrv->driver.remove = ancillary_remove_driver;
- ancildrv->driver.shutdown = ancillary_shutdown_driver;
I think that this part is wrong, probe/remove/shutdown functions should come from ancillary_bus_type.
From checking other usage cases, this is the model that is used for probe, remove, and shutdown in drivers. Here is the example from Greybus.
int greybus_register_driver(struct greybus_driver *driver, struct module *owner, const char *mod_name) { int retval;
if (greybus_disabled()) return -ENODEV; driver->driver.bus = &greybus_bus_type; driver->driver.name = driver->name; driver->driver.probe = greybus_probe; driver->driver.remove = greybus_remove; driver->driver.owner = owner; driver->driver.mod_name = mod_name;You are overwriting private device_driver callbacks that makes impossible to make container_of of ancillary_driver to chain operations.
I am sorry, you lost me here. you cannot perform container_of on the callbacks because they are pointers, but if you are referring to going from device_driver to the auxiliary_driver, that is what happens in auxiliary_probe_driver in the very beginning.
static int auxiliary_probe_driver(struct device *dev) 145 { 146 struct auxiliary_driver *auxdrv = to_auxiliary_drv(dev->driver); 147 struct auxiliary_device *auxdev = to_auxiliary_dev(dev);
Did I miss your meaning?
I think you're misunderstanding the cases when the bus_type.{probe,remove} is used vs the driver.{probe,remove} callbacks. The bus_type callbacks are to implement a pattern where the 'probe' and 'remove' method are typed to the bus device type. For example 'struct pci_dev *' instead of raw 'struct device *'. See this conversion of dax bus as an example of going from raw 'struct device *' typed probe/remove to dax-device typed probe/remove:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?...
Thanks Dan for the reference, very useful. This doesn't look like a a big change to implement, just wondering about the benefits and drawbacks, if any? I am a bit confused here.
First, was the initial pattern wrong as Leon asserted it? Such code exists in multiple examples in the kernel and there's nothing preventing the use of container_of that I can think of. Put differently, if this code was wrong then there are other existing buses that need to be updated.
Second, what additional functionality does this move from driver to bus_type provide? The commit reference just states 'In preparation for introducing seed devices the dax-bus core needs to be able to intercept ->probe() and ->remove() operations", but that doesn't really help me figure out what 'intercept' means. Would you mind elaborating?
And last, the existing probe function does calls dev_pm_domain_attach():
static int ancillary_probe_driver(struct device *dev) { struct ancillary_driver *ancildrv = to_ancillary_drv(dev->driver); struct ancillary_device *ancildev = to_ancillary_dev(dev); int ret;
ret = dev_pm_domain_attach(dev, true);So the need to access the raw device still exists. Is this still legit if the probe() is moved to the bus_type structure?
Sure, of course.
I have no objection to this change if it preserves the same functionality and possibly extends it, just wanted to better understand the reasons for the change and in which cases the bus probe() makes more sense than a driver probe().
Thanks for enlightening the rest of us!
tl;dr: The ops set by the device driver should never be overwritten by the bus, the bus can only wrap them in its own ops.
The reason to use the bus_type is because the bus type is the only agent that knows both how to convert a raw 'struct device *' to the bus's native type, and how to convert a raw 'struct device_driver *' to the bus's native driver type. The driver core does:
if (dev->bus->probe) { ret = dev->bus->probe(dev); } else if (drv->probe) { ret = drv->probe(dev); }
...so that the bus has the first priority for probing a device / wrapping the native driver ops. The bus ->probe, in addition to optionally performing some bus specific pre-work, lets the bus upcast the device to bus-native type.
The bus also knows the types of drivers that will be registered to it, so the bus can upcast the dev->driver to the native type.
So with bus_type based driver ops driver authors can do:
struct auxiliary_device_driver auxdrv { .probe = fn(struct auxiliary_device *, <any aux bus custom probe arguments>) };
auxiliary_driver_register(&auxdrv); <-- the core code can hide bus details
Without bus_type the driver author would need to do:
struct auxiliary_device_driver auxdrv { .drv = { .probe = fn(struct device *), <-- no opportunity for bus specific probe args .bus = &auxilary_bus_type, <-- unnecessary export to device drivers }, };
driver_register(&auxdrv.drv)