netdev - Re: [net-next 1/1] virtual-bus: Implementation of Virtual Bus

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Date:   Tue, 12 Nov 2019 20:08:19 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net,
        Dave Ertman <david.m.ertman@...el.com>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, nhorman@...hat.com,
        sassmann@...hat.com, parav@...lanox.com,
        Kiran Patil <kiran.patil@...el.com>
Subject: Re: [net-next 1/1] virtual-bus: Implementation of Virtual Bus

On Tue, Nov 12, 2019 at 10:28:26PM +0100, Greg KH wrote:

> > + */
> > +struct virtbus_device {
> > +	const char			*name;
> > +	int				id;
> > +	const struct virtbus_dev_id	*dev_id;
> > +	struct device			dev;
> > +	void				*data;
> > +};
> > +
> > +struct virtbus_driver {
> > +	int (*probe)(struct virtbus_device *);
> > +	int (*remove)(struct virtbus_device *);
> > +	void (*shutdown)(struct virtbus_device *);
> > +	int (*suspend)(struct virtbus_device *, pm_message_t state);
> > +	int (*resume)(struct virtbus_device *);
> > +	struct device_driver driver;
> > +	const struct virtbus_dev_id *id_table;
> > +};
> > +
> > +#define virtbus_get_dev_id(vdev)	((vdev)->id_entry)
> > +#define virtbus_get_devdata(dev)	((dev)->devdata)
> 
> What are these for?

As far as I can see, the scheme here, using the language from the most
recent discussion is:

   // in core or netdev module
   int mlx5_core_create()
   {
      struct mlx5_core_dev *core = kzalloc(..)

      [..]

      core->vdev = virtbus_dev_alloc("mlx5_core", core);
   }


   // in rdma module
   static int mlx5_rdma_probe(struct virtbus_device *dev)
   {
        // Get the value passed to virtbus_dev_alloc()
	struct mlx5_core_dev *core = virtbus_get_devdata(dev)

	// Use the huge API surrounding struct mlx5_core_dev
	qp = mlx5_core_create_qp(core, ...);
   }

   static struct virtbus_driver mlx5_rdma_driver = {
      .probe = mlx5_rdma_probe,
      .match = {"mlx5_core"}
   }

Drivers that match "mlx5_core" know that the opaque
'virtbus_get_devdata()' is a 'struct mlx5_core_dev *' and use that
access the core driver.

A "ice_core" would know it is some 'struct ice_core_dev *' for Intel
and uses that pointer, etc.

ie it is just a way to a pass a 'void *' from one module to another
while using the driver core to manage module autoloading and binding.

Jason