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

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Date:   Mon, 11 Nov 2019 15:17:32 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Parav Pandit <parav@...lanox.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        David M <david.m.ertman@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Or Gerlitz <gerlitz.or@...il.com>,
        "Jason Wang (jasowang@...hat.com)" <jasowang@...hat.com>
Subject: Re: [PATCH net-next 00/19] Mellanox, mlx5 sub function support

Sun, Nov 10, 2019 at 08:48:31PM CET, parav@...lanox.com wrote:
>
>> From: Jason Gunthorpe <jgg@...pe.ca>
>> Sent: Friday, November 8, 2019 6:57 PM
>> > We should be creating 3 different buses, instead of mdev bus being de-
>> multiplexer of that?
>> >
>> > Hence, depending the device flavour specified, create such device on right
>> bus?
>> >
>> > For example,
>> > $ devlink create subdev pci/0000:05:00.0 flavour virtio name foo
>> > subdev_id 1 $ devlink create subdev pci/0000:05:00.0 flavour mdev
>> > <uuid> subdev_id 2 $ devlink create subdev pci/0000:05:00.0 flavour
>> > mlx5 id 1 subdev_id 3
>> 
>> I like the idea of specifying what kind of interface you want at sub device
>> creation time. It fits the driver model pretty well and doesn't require abusing
>> the vfio mdev for binding to a netdev driver.
>> 
>> > $ devlink subdev pci/0000:05:00.0/<subdev_id> config <params> $ echo
>> > <respective_device_id> <sysfs_path>/bind
>> 
>> Is explicit binding really needed?
>No.
>
>> If you specify a vfio flavour why shouldn't
>> the vfio driver autoload and bind to it right away? That is kind of the point
>> of the driver model...
>> 
>It some configuration is needed that cannot be passed at device creation time, explicit bind later can be used.
>
>> (kind of related, but I don't get while all that GUID and lifecycle stuff in mdev
>> should apply for something like a SF)
>> 
>GUID is just the name of the device.
>But lets park this aside for a moment.
>
>> > Implement power management callbacks also on all above 3 buses?
>> > Abstract out mlx5_bus into more generic virtual bus (vdev bus?) so
>> > that multiple vendors can reuse?
>> 
>> In this specific case, why does the SF in mlx5 mode even need a bus?
>> Is it only because of devlink? That would be unfortunate
>>
>Devlink is one part due to identifying using bus/dev.
>How do we refer to its devlink instance of SF without bus/device?

Question is, why to have devlink instance for SF itself. Same as VF, you
don't need devlink instance. You only need devlink_port (or
devlink_subdev) instance on the PF devlink parent for it.


>Can we extend devlink_register() to accept optionally have sf_id?
>
>If we don't have a bus, creating sub function (a device), without a 'struct device' which will have BAR, resources, etc is odd.
>
>Now if we cannot see 'struct device' in sysfs, how do we persistently name them?
>Are we ok to add /sys/class/net/sf_netdev/subdev_id
>And
>/sys/class/infiniband/<rdma_dev>/subdev_id
>
>So that systemd/udev can rename them as en<X?><subdev_id> and roce<X><subdev_id>
>If so, what will be X without a bus type?
>
>This route without a bus is certainly helpful to overcome the IOMMU limitation where IOMMU only listens to pci bus type for DMAR setup, 
>dmar_register_bus_notifier(), and in 
>intel_iommu_init()-> bus_set_iommu(&pci_bus_type, &intel_iommu_ops);
>and other IOMMU doing similar PCI/AMBA binding.
>This is currently overcome using WA dma_ops.