linux-kernel - Re: [RFC net-next 0/8] Introducing subdev bus and devlink extension

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Date:   Fri, 8 Mar 2019 02:23:32 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Parav Pandit <parav@...lanox.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     Or Gerlitz <gerlitz.or@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "michal.lkml@...kovi.net" <michal.lkml@...kovi.net>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Jiri Pirko <jiri@...lanox.com>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [RFC net-next 0/8] Introducing subdev bus and devlink extension



<snip>

>>>
>>> Yes. I got my patches to adapt to mdev way. Will be posting RFC v2 soon.
>>> Will wait for a day to receive more comments/views from Greg and others.
>>>
>>> As I explained in this cover-letter and discussion, First use case is
>>> to create and use mdevs in the host (and not in VM).
>>> Later on, I am sure once we have mdevs available, VM users will likely use
>> it.
>>>
>>> So, mlx5_core driver will have two components as starting point.
>>>
>>> 1. drivers/net/ethernet/mellanox/mlx5/core/mdev/mdev.c
>>> This is mdev device life cycle driver which will do, mdev_register_device()
>> and implements mlx5_mdev_ops.
>>>
>> Ok. I would suggest not use mdev.c file name, may be add device name,
>> something like mlx_mdev.c or vfio_mlx.c
>>
> mlx5/core is coding convention is not following to prefix mlx to its 40+ files.
> 
> it uses actual subsystem or functionality name, such as,
> sriov.c
> eswitch.c
> fw.c
> en_tc.c (en for Ethernet)
> lag.c
> so,
> mdev.c aligns to rest of the 40+ files.
> 
> 
>>> 2. drivers/net/ethernet/mellanox/mlx5/core/mdev/mdev_driver.c
>>> This is mdev device driver which does mdev_register_driver() and
>>> probe() creates netdev by heavily reusing existing code of the PF device.
>>> These drivers will not be placed under drivers/vfio/mdev, because this is
>> not a vfio driver.
>>> This is fine, right?
>>>
>>
>> I'm not too familiar with netdev, but can you create netdev on open() call on
>> mlx mdev device? Then you don't have to write mdev device driver.
>>
> Who invokes open() and release()?
> I believe it is the qemu would do open(), release, read/write/mmap?
> 
> Assuming that is the case,
> I think its incorrect to create netdev in open.
> Because when we want to map the mdev to VM using above mdev calls, we actually wont be creating netdev in host.
> Instead, some queues etc will be setup as part of these calls.
> 
> By default this created mdev is bound to vfio_mdev.
> And once we unbind the device from this driver, we need to bind to mlx5 driver so that driver can create the netdev etc.
> 
> Or did I get open() and friends call wrong?
> 

In 'struct mdev_parent_ops' there are create() and remove(). When user
creates mdev device by writing UUID to create sysfs, vendor driver's
create() callback gets called. This should be used to allocate/commit
resources from parent device and on remove() callback free those
resources. So there is no need to bind mlx5 driver to that mdev device.

open/release/read/write/mmap/ioctl are regular file operations for that
mdev device.

Thanks,
Kirti