RE: [PATCH v2 1/6] Add ancillary bus support

From: Parav Pandit <parav@nvidia.com>
To: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	Dan Williams <dan.j.williams@intel.com>
Cc: Leon Romanovsky <leon@kernel.org>,
	"Ertman, David M" <david.m.ertman@intel.com>,
	Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
	"alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
	"parav@mellanox.com" <parav@mellanox.com>,
	"tiwai@suse.de" <tiwai@suse.de>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"ranjani.sridharan@linux.intel.com" 
	<ranjani.sridharan@linux.intel.com>,
	"fred.oh@linux.intel.com" <fred.oh@linux.intel.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	"dledford@redhat.com" <dledford@redhat.com>,
	"broonie@kernel.org" <broonie@kernel.org>,
	Jason Gunthorpe <jgg@nvidia.com>,
	"kuba@kernel.org" <kuba@kernel.org>,
	"Saleem, Shiraz" <shiraz.saleem@intel.com>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"Patil, Kiran" <kiran.patil@intel.com>
Subject: RE: [PATCH v2 1/6] Add ancillary bus support
Date: Thu, 8 Oct 2020 11:10:25 +0000	[thread overview]
Message-ID: <BY5PR12MB432291F0683A2295170C2F3BDC0B0@BY5PR12MB4322.namprd12.prod.outlook.com> (raw)
In-Reply-To: <20201008075048.GA254837@kroah.com>

> From: gregkh@linuxfoundation.org <gregkh@linuxfoundation.org>
> Sent: Thursday, October 8, 2020 1:21 PM
> 
> On Thu, Oct 08, 2020 at 12:38:00AM -0700, Dan Williams wrote:
> > On Thu, Oct 8, 2020 at 12:01 AM Leon Romanovsky <leon@kernel.org>
> wrote:
> > [..]
> > > All stated above is my opinion, it can be different from yours.
> >
> > Yes, but we need to converge to move this forward. Jason was involved
> > in the current organization for registration, Greg was angling for
> > this to be core functionality. I have use cases outside of RDMA and
> > netdev. Parav was ok with the current organization. The SOF folks
> > already have a proposed incorporation of it. The argument I am hearing
> > is that "this registration api seems hard for driver writers" when we
> > have several driver writers who have already taken a look and can make
> > it work. If you want to follow on with a simpler wrappers for your use
> > case, great, but I do not yet see anyone concurring with your opinion
> > that the current organization is irretrievably broken or too obscure
> > to use.
> 
> That's kind of because I tuned out of this thread a long time ago :)
> 
> I do agree with Leon that I think the current patch is not the correct way to
> do this the easiest, but don't have a competing proposal to show what I
> mean.
> 
> Yet.
Please consider the approach of ib_alloc_device(), ib_dealloc_device() and ib_register_register()/unregister().
(a) It avoids driver calling put_device() on error unwinding path.
(b) still achieves container_of().

> 
> Let's see what happens after 5.10-rc1 is out, it's too late now for any of this
> for this next merge window so we can not worry about it for a few weeks.
> 
Ok. INHO giving direction to Dave and others to either refine current APIs or follow ib_alloc_device() approach will be a helpful input.

ancillary bus can do better APIs than the newly (march 2020 !) introduced vdpa bus [1] and its drivers which follows put_device() pattern in [2] and [3] in error unwinding path.

[1] https://elixir.bootlin.com/linux/v5.9-rc8/source/drivers/vdpa/vdpa.c
[2] https://elixir.bootlin.com/linux/v5.9-rc8/source/drivers/vdpa/ifcvf/ifcvf_main.c#L475
[3] https://elixir.bootlin.com/linux/v5.9-rc8/source/drivers/vdpa/mlx5/net/mlx5_vnet.c#L1967

> thanks,
> 
> greg k-h