[PATCH v2 1/6] Add ancillary bus support
Parav Pandit
parav at nvidia.com
Thu Oct 8 11:45:29 CEST 2020
> From: Leon Romanovsky <leon at kernel.org>
> Sent: Thursday, October 8, 2020 1:15 PM
>
> 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 }
Yes, subfunction code is also very similar.
You expressed concerned that you didn't like put_device() at [1].
But in above code is touching adev->dev.{parent, release} is ok?
> 254 adev->dev.parent = dev->device;
> 255 adev->dev.release = adev_release;
If not,
We can make it elegant by doing,
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 [2] also eliminates exposing adev.dev.release = <drivers_release_method_to_free_adev> in drivers.
And container_of() benefit also continues..
[1] https://lore.kernel.org/linux-rdma/20201007192610.GD3964015@unreal/
[2] https://elixir.bootlin.com/linux/v5.9-rc8/source/include/rdma/ib_verbs.h#L2791
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