[PATCH v2 1/6] Add ancillary bus support

[Dan Williams]

On Thu, Oct 8, 2020 at 3:04 PM Ertman, David M <david.m.ertman at intel.com> wrote:
>
> > -----Original Message-----
> > From: Leon Romanovsky <leon at kernel.org>
> > Sent: Tuesday, October 6, 2020 10:23 AM
> > To: Ertman, David M <david.m.ertman at intel.com>
> > Cc: alsa-devel at alsa-project.org; tiwai at suse.de; broonie at kernel.org; linux-
> > rdma at vger.kernel.org; jgg at nvidia.com; dledford at redhat.com;
> > netdev at vger.kernel.org; davem at davemloft.net; kuba at kernel.org;
> > gregkh at linuxfoundation.org; ranjani.sridharan at linux.intel.com; pierre-
> > louis.bossart at linux.intel.com; fred.oh at linux.intel.com;
> > parav at mellanox.com; Saleem, Shiraz <shiraz.saleem at intel.com>; Williams,
> > Dan J <dan.j.williams at intel.com>; Patil, Kiran <kiran.patil at intel.com>
> > Subject: Re: [PATCH v2 1/6] Add ancillary bus support
> >
> > On Mon, Oct 05, 2020 at 11:24:41AM -0700, Dave Ertman wrote:
> > > Add support for the Ancillary Bus, ancillary_device and ancillary_driver.
> > > It enables drivers to create an ancillary_device and bind an
> > > ancillary_driver to it.
> > >
> > > The bus supports probe/remove shutdown and suspend/resume callbacks.
> > > Each ancillary_device has a unique string based id; driver binds to
> > > an ancillary_device based on this id through the bus.
> > >
> > > Co-developed-by: Kiran Patil <kiran.patil at intel.com>
> > > Signed-off-by: Kiran Patil <kiran.patil at intel.com>
> > > Co-developed-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>
> > > Signed-off-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>
> > > Co-developed-by: Fred Oh <fred.oh at linux.intel.com>
> > > Signed-off-by: Fred Oh <fred.oh at linux.intel.com>
> > > Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> > > Reviewed-by: Shiraz Saleem <shiraz.saleem at intel.com>
> > > Reviewed-by: Parav Pandit <parav at mellanox.com>
> > > Reviewed-by: Dan Williams <dan.j.williams at intel.com>
> > > Signed-off-by: Dave Ertman <david.m.ertman at intel.com>
> > > ---
> >
> > <...>
> >
> > > +/**
> > > + * __ancillary_driver_register - register a driver for ancillary bus devices
> > > + * @ancildrv: ancillary_driver structure
> > > + * @owner: owning module/driver
> > > + */
> > > +int __ancillary_driver_register(struct ancillary_driver *ancildrv, struct
> > module *owner)
> > > +{
> > > +   if (WARN_ON(!ancildrv->probe) || WARN_ON(!ancildrv->remove)
> > ||
> > > +       WARN_ON(!ancildrv->shutdown) || WARN_ON(!ancildrv-
> > >id_table))
> > > +           return -EINVAL;
> >
> > In our driver ->shutdown is empty, it will be best if ancillary bus will
> > do "if (->remove) ..->remove()" pattern.
> >
>
> Yes, looking it over, only the probe needs to mandatory.  I will change the others to the
> conditional model, and adjust the WARN_ONs.
>
>
> > > +
> > > +   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/?id=75797273189d