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

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Date:   Thu, 19 Mar 2020 11:49:52 +0000
From:   Martin Habets <mhabets@...arflare.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, 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 21/02/2020 18:04, Jason Gunthorpe wrote:
> 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);

I'd like to see something like this as well. In my experiments for a single type of device I've been doing this,
which works fine but is not future-proof:

	struct sfc_rdma_dev *rdev;

	rdev = kzalloc(sizeof(*rdev), GFP_KERNEL);
	if (!rdev)
		return -ENOMEM;

	/* This is like virtbus_dev_alloc() but using our own memory. */
	rdev->vdev.name = SFC_RDMA_DEVNAME;
	rdev->vdev.data = (void *) &rdma_devops;
	rdev->vdev.dev.release = efx_rdma_dev_release;

Martin