Re: [PATCH net-next 00/19] Mellanox, mlx5 sub function support

From: Jiri Pirko <jiri@resnulli.us>
To: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
	Jakub Kicinski <jakub.kicinski@netronome.com>,
	Parav Pandit <parav@mellanox.com>,
	David M <david.m.ertman@intel.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Saeed Mahameed <saeedm@mellanox.com>,
	"kwankhede@nvidia.com" <kwankhede@nvidia.com>,
	"leon@kernel.org" <leon@kernel.org>,
	"cohuck@redhat.com" <cohuck@redhat.com>,
	Jiri Pirko <jiri@mellanox.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	Or Gerlitz <gerlitz.or@gmail.com>
Subject: Re: [PATCH net-next 00/19] Mellanox, mlx5 sub function support
Date: Sat, 9 Nov 2019 12:18:09 +0100	[thread overview]
Message-ID: <20191109111809.GA9565@nanopsycho> (raw)
In-Reply-To: <20191109084659.GB1289838@kroah.com>

Sat, Nov 09, 2019 at 09:46:59AM CET, gregkh@linuxfoundation.org wrote:
>On Fri, Nov 08, 2019 at 08:44:26PM -0400, Jason Gunthorpe wrote:
>> There has been some lack of clarity on what the ?? should be. People
>> have proposed platform and MFD, and those seem to be no-goes. So, it
>> looks like ?? will be a mlx5_driver on a mlx5_bus, and Intel will use
>> an ice_driver on a ice_bus, ditto for cxgb4, if I understand Greg's
>> guidance.
>
>Yes, that is the only way it can work because you really are just
>sharing a single PCI device in a vendor-specific way, and they all need
>to get along with each one properly for that vendor-specific way.  So
>each vendor needs its own "bus" to be able to work out things properly,
>I doubt you can make this more generic than that easily.
>
>> Though I'm wondering if we should have a 'multi_subsystem_device' that
>> was really just about passing a 'void *core_handle' from the 'core'
>> (ie the bus) to the driver (ie RDMA, netdev, etc). 
>
>Ick, no.
>
>> It seems weakly defined, but also exactly what every driver doing this
>> needs.. It is basically what this series is abusing mdev to accomplish.
>
>What is so hard about writing a bus?  Last I tried it was just a few
>hundred lines of code, if that.  I know it's not the easiest in places,
>but we have loads of examples to crib from.  If you have
>problems/questions, just ask!
>
>Or, worst case, you just do what I asked in this thread somewhere, and
>write a "virtual bus" where you just create devices and bind them to the
>driver before registering and away you go.  No auto-loading needed (or
>possible), but then you have a generic layer that everyone can use if
>they want to (but you loose some functionality at the expense of
>generic code.)

Pardon my ignorance, just to be clear: You suggest to have
one-virtual-bus-per-driver or rather some common "xbus" to serve this
purpose for all of them, right?
If so, isn't that a bit ugly to have a bus in every driver? I wonder if
there can be some abstraction found.

>
>Are these constant long email threads a way that people are just trying
>to get me to do this work for them?  Because if it is, it's working...

Maybe they are just confused, like I am :)

>
>thanks,
>
>greg k-h