netdev - Re: [RFC PATCH v4 10/25] RDMA/irdma: Add driver framework definitions

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Date:   Fri, 21 Feb 2020 14:04:27 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Parav Pandit <parav@...lanox.com>
Cc:     "Saleem, Shiraz" <shiraz.saleem@...el.com>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Ismail, Mustafa" <mustafa.ismail@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "sassmann@...hat.com" <sassmann@...hat.com>
Subject: Re: [RFC PATCH v4 10/25] RDMA/irdma: Add driver framework definitions

On Fri, Feb 21, 2020 at 05:23:31PM +0000, Parav Pandit wrote:
> On 2/21/2020 11:01 AM, Saleem, Shiraz wrote:
> >> Subject: RE: [RFC PATCH v4 10/25] RDMA/irdma: Add driver framework
> >> definitions
> >>
> > 
> > [....]
> > 
> >>>>> +static int irdma_devlink_reload_up(struct devlink *devlink,
> >>>>> +				   struct netlink_ext_ack *extack) {
> >>>>> +	struct irdma_dl_priv *priv = devlink_priv(devlink);
> >>>>> +	union devlink_param_value saved_value;
> >>>>> +	const struct virtbus_dev_id *id = priv->vdev->matched_element;
> >>>>
> >>>> Like irdma_probe(), struct iidc_virtbus_object *vo is accesible for
> >>>> the given
> >>> priv.
> >>>> Please use struct iidc_virtbus_object for any sharing between two drivers.
> >>>> matched_element modification inside the virtbus match() function and
> >>>> accessing pointer to some driver data between two driver through
> >>>> this matched_element is not appropriate.
> >>>
> >>> We can possibly avoid matched_element and driver data look up here.
> >>> But fundamentally, at probe time (see irdma_gen_probe) the irdma
> >>> driver needs to know which generation type of vdev we bound to. i.e. i40e or ice
> >> ?
> >>> since we support both.
> >>> And based on it, extract the driver specific virtbus device object,
> >>> i.e i40e_virtbus_device vs iidc_virtbus_object and init that device.
> >>>
> >>> Accessing driver_data off the vdev matched entry in
> >>> irdma_virtbus_id_table is how we know this generation info and make the
> >> decision.
> >>>
> >> If there is single irdma driver for two different virtbus device types, it is better to
> >> have two instances of virtbus_register_driver() with different matching string/id.
> >> So based on the probe(), it will be clear with virtbus device of interest got added.
> >> This way, code will have clear separation between two device types.
> > 
> > Thanks for the feedback!
> > Is it common place to have multiple driver_register instances of same bus type
> > in a driver to support different devices? Seems odd.
> > Typically a single driver that supports multiple device types for a specific bus-type
> > would do a single bus-specific driver_register and pass in an array of bus-specific
> > device IDs and let the bus do the match up for you right? And in the probe(), a driver could do device
> > specific quirks for the device types. Isnt that purpose of device ID tables for pci, platform, usb etc?
> > Why are we trying to handle multiple virtbus device types from a driver any differently?
> > 
> 
> If differences in treating the two devices is not a lot, if you have lot
> of common code, it make sense to do single virtbus_register_driver()
> with two different ids.
> In that case, struct virtbus_device_id should have some device specific
> field like how pci has driver_data.
> 
> It should not be set by the match() function by virtbus core.
> This field should be setup in the id table by the hw driver which
> invokes virtbus_register_device().

Yes

I think the basic point here is that the 'id' should specify what
container_of() is valid on the virtbus_device

And for things like this where we want to make a many to one
connection then it makes sense to permute the id for each 'connection
point'

ie, if the id was a string like OF uses maybe you'd have

 intel,i40e,rdma
 intel,i40e,ethernet
 intel,ice,rdma

etc

A string for match id is often a good idea..

And I'd suggest introducing a matching alloc so it is all clear and
type safe:

   struct mydev_struct mydev;

   mydev = virtbus_alloc(parent, "intel,i40e,rdma", struct mydev_struct,
                         vbus_dev);


   [..]
   virtbus_register(&mydev->vbus_dev);

Jason