[PATCH v2 1/6] Add ancillary bus support

[Ertman, David M]

> -----Original Message-----
> From: Dan Williams <dan.j.williams at intel.com>
> Sent: Wednesday, October 7, 2020 11:32 PM
> To: Leon Romanovsky <leon at kernel.org>
> Cc: Ertman, David M <david.m.ertman at intel.com>; Parav Pandit
> <parav at nvidia.com>; Pierre-Louis Bossart <pierre-
> louis.bossart at linux.intel.com>; alsa-devel at alsa-project.org;
> parav at mellanox.com; tiwai at suse.de; netdev at vger.kernel.org;
> ranjani.sridharan at linux.intel.com; fred.oh at linux.intel.com; linux-
> rdma at vger.kernel.org; dledford at redhat.com; broonie at kernel.org; Jason
> Gunthorpe <jgg at nvidia.com>; gregkh at linuxfoundation.org;
> kuba at kernel.org; Saleem, Shiraz <shiraz.saleem at intel.com>;
> davem at davemloft.net; Patil, Kiran <kiran.patil at intel.com>
> Subject: Re: [PATCH v2 1/6] Add ancillary bus support
> 
> On Wed, Oct 7, 2020 at 10:21 PM Leon Romanovsky <leon at kernel.org>
> wrote:
> >
> > On Wed, Oct 07, 2020 at 08:46:45PM +0000, Ertman, David M wrote:
> > > > -----Original Message-----
> > > > From: Parav Pandit <parav at nvidia.com>
> > > > Sent: Wednesday, October 7, 2020 1:17 PM
> > > > To: Leon Romanovsky <leon at kernel.org>; Ertman, David M
> > > > <david.m.ertman at intel.com>
> > > > Cc: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>; alsa-
> > > > devel at alsa-project.org; parav at mellanox.com; tiwai at suse.de;
> > > > netdev at vger.kernel.org; ranjani.sridharan at linux.intel.com;
> > > > fred.oh at linux.intel.com; linux-rdma at vger.kernel.org;
> > > > dledford at redhat.com; broonie at kernel.org; Jason Gunthorpe
> > > > <jgg at nvidia.com>; gregkh at linuxfoundation.org; kuba at kernel.org;
> Williams,
> > > > Dan J <dan.j.williams at intel.com>; Saleem, Shiraz
> > > > <shiraz.saleem at intel.com>; davem at davemloft.net; Patil, Kiran
> > > > <kiran.patil at intel.com>
> > > > Subject: RE: [PATCH v2 1/6] Add ancillary bus support
> > > >
> > > >
> > > > > From: Leon Romanovsky <leon at 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?
> >
> > Let me summarize.
> > 1. You are not providing driver/core API but simplification and obfuscation
> > of basic primitives and structures. This is new layer. There is no room for
> > a claim that we must to follow internal API.
> 
> Yes, this a driver core api, Greg even questioned why it was in
> drivers/bus instead of drivers/base which I think makes sense.

Will move to drivers/base with next patch set.

-DaveE