[PATCH v2 1/6] Add ancillary bus support
Leon Romanovsky
leon at kernel.org
Thu Oct 8 09:45:25 CEST 2020
On Thu, Oct 08, 2020 at 07:14:17AM +0000, Parav Pandit wrote:
>
>
> > From: Leon Romanovsky <leon at kernel.org>
> > Sent: Thursday, October 8, 2020 10:56 AM
> >
> > On Thu, Oct 08, 2020 at 04:56:01AM +0000, Parav Pandit wrote:
> > >
> > >
> > > > From: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> > > > Sent: Thursday, October 8, 2020 3:20 AM
> > > >
> > > >
> > > > On 10/7/20 4:22 PM, Ertman, David M wrote:
> > > > >> -----Original Message-----
> > > > >> From: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> > > > >> Sent: Wednesday, October 7, 2020 1:59 PM
> > > > >> To: Ertman, David M <david.m.ertman at intel.com>; Parav Pandit
> > > > >> <parav at nvidia.com>; Leon Romanovsky <leon at kernel.org>
> > > > >> Cc: 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
> > > > >>
> > > > >>
> > > > >>
> > > > >>>> 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.
> > > > >>
> > > > >> Kind reminder that we introduced the two functions to allow the
> > > > >> caller to know if it needed to free memory when initialize()
> > > > >> fails, and it didn't need to free memory when add() failed since
> > > > >> put_device() takes care of it. If you have a single init()
> > > > >> function it's impossible to know which behavior to select on error.
> > > > >>
> > > > >> I also have a case with SoundWire where it's nice to first
> > > > >> initialize, then set some data and then add.
> > > > >>
> > > > >
> > > > > The flow as outlined by Parav above does an initialize as the
> > > > > first step, so every error path out of the function has to do a
> > > > > put_device(), so you would never need to manually free the memory
> > > > > in
> > > > the setup function.
> > > > > It would be freed in the release call.
> > > >
> > > > err = ancillary_device_initialize(); if (err)
> > > > return ret;
> > > >
> > > > where is the put_device() here? if the release function does any
> > > > sort of kfree, then you'd need to do it manually in this case.
> > > Since device_initialize() failed, put_device() cannot be done here.
> > > So yes, pseudo code should have shown, if (err) {
> > > kfree(adev);
> > > return err;
> > > }
> > >
> > > If we just want to follow register(), unregister() pattern,
> > >
> > > Than,
> > >
> > > ancillar_device_register() should be,
> > >
> > > /**
> > > * ancillar_device_register() - register an ancillary device
> > > * NOTE: __never directly free @adev after calling this function, even
> > > if it returned
> > > * an error. Always use ancillary_device_put() to give up the reference
> > initialized by this function.
> > > * This note matches with the core and caller knows exactly what to be
> > done.
> > > */
> > > ancillary_device_register()
> > > {
> > > device_initialize(&adev->dev);
> > > if (!dev->parent || !adev->name)
> > > return -EINVAL;
> > > if (!dev->release && !(dev->type && dev->type->release)) {
> > > /* core is already capable and throws the warning when
> > release callback is not set.
> > > * It is done at drivers/base/core.c:1798.
> > > * For NULL release it says, "does not have a release()
> > function, it is broken and must be fixed"
> > > */
> > > return -EINVAL;
> > > }
> > > err = dev_set_name(adev...);
> > > if (err) {
> > > /* kobject_release() -> kobject_cleanup() are capable to
> > detect if name is set/ not set
> > > * and free the const if it was set.
> > > */
> > > return err;
> > > }
> > > err = device_add(&adev->dev);
> > > If (err)
> > > return err;
> > > }
> > >
> > > Caller code:
> > > init()
> > > {
> > > adev = kzalloc(sizeof(*foo_adev)..);
> > > if (!adev)
> > > return -ENOMEM;
> > > err = ancillary_device_register(&adev);
> > > if (err)
> > > goto err;
> > >
> > > err:
> > > ancillary_device_put(&adev);
> > > return err;
> > > }
> > >
> > > cleanup()
> > > {
> > > ancillary_device_unregister(&adev);
> > > }
> > >
> > > Above pattern is fine too matching the core.
> > >
> > > If I understand Leon correctly, he prefers simple register(), unregister()
> > pattern.
> > > If, so it should be explicit register(), unregister() API.
> >
> > This is my summary
> > https://lore.kernel.org/linux-rdma/20201008052137.GA13580@unreal
> > The API should be symmetric.
> >
>
> I disagree to your below point.
> > 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.
> If ancillary bus has
> ancillary_device_add(), it cannot do device_initialize() and device_add() in both.
>
> I provided two examples and what really matters is a given patchset uses (need to use) which pattern,
> initialize() + add(), or register() + unregister().
>
> As we all know that API is not added for future. It is the future patch extends it.
> So lets wait for Pierre to reply if soundwire can follow register(), unregister() sequence.
> This way same APIs can service both use-cases.
>
> Regarding,
> > 3. You can't "ask" from users to call internal calls (put_device) over internal
> > fields in ancillary_device.
> In that case if should be ancillary_device_put() ancillary_device_release().
>
> Or we should follow the patten of ib_alloc_device [1],
> ancillary_device_alloc()
> -> kzalloc(adev + dev) with compile time assert check like rdma and vdpa subsystem.
> ->device_initialize()
> ancillary_device_add()
>
> ancillar_device_de() <- balances with add
> ancillary_device_dealloc() <-- balances with device_alloc(), which does the put_device() + free the memory allocated in alloc().
>
> This approach of [1] also eliminates exposing adev.dev.release = <drivers_release_method_to_free_adev> in drivers.
> And container_of() benefit also continues..
>
> [1] https://elixir.bootlin.com/linux/v5.9-rc8/source/include/rdma/ib_verbs.h#L2791
>
My code looks like this, probably yours looks the same.
247 priv->adev[i] = kzalloc(sizeof(*priv->adev[i]), GFP_KERNEL);
248 if (!priv->adev[i])
249 goto init_err;
250
251 adev = &priv->adev[i]->adev;
252 adev->id = idx;
253 adev->name = mlx5_adev_devices[i].suffix;
254 adev->dev.parent = dev->device;
255 adev->dev.release = adev_release;
256 priv->adev[i]->mdev = dev;
257
258 ret = ancillary_device_initialize(adev);
259 if (ret)
260 goto init_err;
261
262 ret = ancillary_device_add(adev);
263 if (ret) {
264 put_device(&adev->dev);
265 goto add_err;
266 }
Thanks
More information about the Alsa-devel
mailing list