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Date: Thu, 8 Oct 2020 08:21:37 +0300 From: Leon Romanovsky <leon@...nel.org> To: "Ertman, David M" <david.m.ertman@...el.com> Cc: Parav Pandit <parav@...dia.com>, Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>, "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>, "parav@...lanox.com" <parav@...lanox.com>, "tiwai@...e.de" <tiwai@...e.de>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "ranjani.sridharan@...ux.intel.com" <ranjani.sridharan@...ux.intel.com>, "fred.oh@...ux.intel.com" <fred.oh@...ux.intel.com>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>, "dledford@...hat.com" <dledford@...hat.com>, "broonie@...nel.org" <broonie@...nel.org>, Jason Gunthorpe <jgg@...dia.com>, "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, "kuba@...nel.org" <kuba@...nel.org>, "Williams, Dan J" <dan.j.williams@...el.com>, "Saleem, Shiraz" <shiraz.saleem@...el.com>, "davem@...emloft.net" <davem@...emloft.net>, "Patil, Kiran" <kiran.patil@...el.com> Subject: Re: [PATCH v2 1/6] Add ancillary bus support On Wed, Oct 07, 2020 at 08:46:45PM +0000, Ertman, David M wrote: > > -----Original Message----- > > From: Parav Pandit <parav@...dia.com> > > Sent: Wednesday, October 7, 2020 1:17 PM > > To: Leon Romanovsky <leon@...nel.org>; Ertman, David M > > <david.m.ertman@...el.com> > > Cc: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>; alsa- > > devel@...a-project.org; parav@...lanox.com; tiwai@...e.de; > > netdev@...r.kernel.org; ranjani.sridharan@...ux.intel.com; > > fred.oh@...ux.intel.com; linux-rdma@...r.kernel.org; > > dledford@...hat.com; broonie@...nel.org; Jason Gunthorpe > > <jgg@...dia.com>; gregkh@...uxfoundation.org; kuba@...nel.org; Williams, > > Dan J <dan.j.williams@...el.com>; Saleem, Shiraz > > <shiraz.saleem@...el.com>; davem@...emloft.net; Patil, Kiran > > <kiran.patil@...el.com> > > Subject: RE: [PATCH v2 1/6] Add ancillary bus support > > > > > > > From: Leon Romanovsky <leon@...nel.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. 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(). 3. You can't "ask" from users to call internal calls (put_device) over internal fields in ancillary_device. 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/). Thanks > > -DaveE
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