RE: [PATCH v2 1/6] Add ancillary bus support

["Ertman, David M" <david.m.ertman@intel.com>]

> -----Original Message-----
> From: Parav Pandit <parav@nvidia.com>
> Sent: Wednesday, October 7, 2020 1:17 PM
> To: Leon Romanovsky <leon@kernel.org>; Ertman, David M
> <david.m.ertman@intel.com>
> Cc: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>; alsa-
> devel@alsa-project.org; parav@mellanox.com; tiwai@suse.de;
> netdev@vger.kernel.org; ranjani.sridharan@linux.intel.com;
> fred.oh@linux.intel.com; linux-rdma@vger.kernel.org;
> dledford@redhat.com; broonie@kernel.org; Jason Gunthorpe
> <jgg@nvidia.com>; gregkh@linuxfoundation.org; kuba@kernel.org; Williams,
> Dan J <dan.j.williams@intel.com>; Saleem, Shiraz
> <shiraz.saleem@intel.com>; davem@davemloft.net; Patil, Kiran
> <kiran.patil@intel.com>
> Subject: RE: [PATCH v2 1/6] Add ancillary bus support
> 
> 
> > From: Leon Romanovsky <leon@kernel.org>
> > Sent: Thursday, October 8, 2020 12:56 AM
> >
> > > > This API is partially obscures low level driver-core code and needs
> > > > to provide clear and proper abstractions without need to remember
> > > > about put_device. There is already _add() interface why don't you do
> > > > put_device() in it?
> > > >
> > >
> > > The pushback Pierre is referring to was during our mid-tier internal
> > > review.  It was primarily a concern of Parav as I recall, so he can speak to
> his
> > reasoning.
> > >
> > > What we originally had was a single API call
> > > (ancillary_device_register) that started with a call to
> > > device_initialize(), and every error path out of the function performed a
> > put_device().
> > >
> > > Is this the model you have in mind?
> >
> > I don't like this flow:
> > ancillary_device_initialize()
> > if (ancillary_ancillary_device_add()) {
> >   put_device(....)
> >   ancillary_device_unregister()
> Calling device_unregister() is incorrect, because add() wasn't successful.
> Only put_device() or a wrapper ancillary_device_put() is necessary.
> 
> >   return err;
> > }
> >
> > And prefer this flow:
> > ancillary_device_initialize()
> > if (ancillary_device_add()) {
> >   ancillary_device_unregister()
> This is incorrect and a clear deviation from the current core APIs that adds the
> confusion.
> 
> >   return err;
> > }
> >
> > In this way, the ancillary users won't need to do non-intuitive put_device();
> 
> Below is most simple, intuitive and matching with core APIs for name and
> design pattern wise.
> init()
> {
> 	err = ancillary_device_initialize();
> 	if (err)
> 		return ret;
> 
> 	err = ancillary_device_add();
> 	if (ret)
> 		goto err_unwind;
> 
> 	err = some_foo();
> 	if (err)
> 		goto err_foo;
> 	return 0;
> 
> err_foo:
> 	ancillary_device_del(adev);
> err_unwind:
> 	ancillary_device_put(adev->dev);
> 	return err;
> }
> 
> cleanup()
> {
> 	ancillary_device_de(adev);
> 	ancillary_device_put(adev);
> 	/* It is common to have a one wrapper for this as
> ancillary_device_unregister().
> 	 * This will match with core device_unregister() that has precise
> documentation.
> 	 * but given fact that init() code need proper error unwinding, like
> above,
> 	 * it make sense to have two APIs, and no need to export another
> symbol for unregister().
> 	 * This pattern is very easy to audit and code.
> 	 */
> }

I like this flow +1

But ... since the init() function is performing both device_init and
device_add - it should probably be called ancillary_device_register, 
and we are back to a single exported API for both register and
unregister.

At that point, do we need wrappers on the primitives init, add, del,
and put?

-DaveE