On Wed, Oct 7, 2020 at 10:21 PM Leon Romanovsky <leon@xxxxxxxxxx> wrote: > > On Wed, Oct 07, 2020 at 08:46:45PM +0000, Ertman, David M wrote: > > > -----Original Message----- > > > From: Parav Pandit <parav@xxxxxxxxxx> > > > Sent: Wednesday, October 7, 2020 1:17 PM > > > To: Leon Romanovsky <leon@xxxxxxxxxx>; Ertman, David M > > > <david.m.ertman@xxxxxxxxx> > > > Cc: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>; alsa- > > > devel@xxxxxxxxxxxxxxxx; parav@xxxxxxxxxxxx; tiwai@xxxxxxx; > > > netdev@xxxxxxxxxxxxxxx; ranjani.sridharan@xxxxxxxxxxxxxxx; > > > fred.oh@xxxxxxxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx; > > > dledford@xxxxxxxxxx; broonie@xxxxxxxxxx; Jason Gunthorpe > > > <jgg@xxxxxxxxxx>; gregkh@xxxxxxxxxxxxxxxxxxx; kuba@xxxxxxxxxx; Williams, > > > Dan J <dan.j.williams@xxxxxxxxx>; Saleem, Shiraz > > > <shiraz.saleem@xxxxxxxxx>; davem@xxxxxxxxxxxxx; Patil, Kiran > > > <kiran.patil@xxxxxxxxx> > > > Subject: RE: [PATCH v2 1/6] Add ancillary bus support > > > > > > > > > > From: Leon Romanovsky <leon@xxxxxxxxxx> > > > > 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. > 2. API should be symmetric. If you call to _register()/_add(), you will need > to call to _unregister()/_del(). Please don't add obscure _put(). It's not obscure it's a long standing semantic for how to properly handle device_add() failures. Especially in this case where there is no way to have something like a common auxiliary_device_alloc() that will work for everyone the only other option is require all device destruction to go through the provided release method (put_device()) after a device_add() failure. > 3. You can't "ask" from users to call internal calls (put_device) over internal > fields in ancillary_device. Sure it can. platform_device_add() requires a put_device() on failure, but also note how platform_device_add() *requires* platform_device_alloc() be used to create the device. That inflexibility is something this auxiliary bus is trying to avoid. > 4. This API should be clear to drivers authors, "device_add()" call (and > semantic) is not used by the drivers (git grep " device_add(" drivers/). This shows 141 instances for me, so I'm not sure what you're getting at? Look, this api is meant to be a replacement for places where platform devices were being abused. The device_initialize() + customize device + device_add() organization has the flexibility needed to let users customize naming and other parts of device creation in a way that a device_register() flow, or platform_device_{register,add} in particular, did not. If the concern is that you'd like to have an auxiliary_device_put() for symmetry that would need to come with the same warning as commented on platform_device_put(), i.e. that's it's really only vanity symmetry to be used in error paths. The semantics of device_add() and device_put() on failure are long established, don't invent new behavior for auxiliary_device_add() and auxiliary_device_put() / put_device().