Subject: RE: [PATCH v4 resend 01/23] iidc: Introduce iidc.h

From: "Saleem, Shiraz" <[email-masked]>
Date: Mon, 12 Apr 2021 14:51:18 +0000

> Subject: Re: [PATCH v4 resend 01/23] iidc: Introduce iidc.h
> 
> On Tue, Apr 06, 2021 at 07:14:40PM -0500, Shiraz Saleem wrote:
> > +/* Structure representing auxiliary driver tailored information about
> > +the core
> > + * PCI dev, each auxiliary driver using the IIDC interface will have
> > +an
> > + * instance of this struct dedicated to it.
> > + */
> > +struct iidc_core_dev_info {
> > +	struct pci_dev *pdev; /* PCI device of corresponding to main function */
> > +	struct auxiliary_device *adev;
> > +	/* KVA / Linear address corresponding to BAR0 of underlying
> > +	 * pci_device.
> > +	 */
> > +	u8 __iomem *hw_addr;
> > +	int cdev_info_id;
> > +
> > +	u8 ftype;	/* PF(false) or VF (true) */
> 
> Where is ftype initialized?

Today it is just pf. But the upcoming Intel ethernet VF driver will set it to true.

> 
> > +	u16 vport_id;
> > +	enum iidc_rdma_protocol rdma_protocol;
> 
> This duplicates the aux device name, not really sure why it is needed. One user just
> uses it to make the string, the rest is entangled with the devlink and doesn't need
> to be stored here.

It is used to pass the type of protocol at drv.probe() in aux RDMA driver.

> 
> > +	struct iidc_qos_params qos_info;
> > +	struct net_device *netdev;
> > +
> > +	struct msix_entry *msix_entries;
> > +	u16 msix_count; /* How many vectors are reserved for this device */
> > +
> > +	/* Following struct contains function pointers to be initialized
> > +	 * by core PCI driver and called by auxiliary driver
> > +	 */
> > +	const struct iidc_core_ops *ops;
> > +};
> 
> I spent a while trying to understand this struct and why it exists and..
> 
> > +
> > +struct iidc_auxiliary_dev {
> > +	struct auxiliary_device adev;
> > +	struct iidc_core_dev_info *cdev_info;
> 
> This cdev_info should just be a 'struct ice_pf *' and the "struct iidc_core_dev_info"
> should be deleted entirely. You'll notice this ends up looking nearly exactly like
> mlx5 does after this.

It was intentionally designed to be core device object carving out only pieces of the PF
information required by the rdma driver. The next near-term PCI driver using IIDC can also
this. Why expose the whole PF? This is a design choice no? Why do we need to follow mlx5?

> 
> You can see it clearly based on how this gets initialized:
> 
> 		cdev_info->pdev = pf->pdev;
> 		cdev_info->hw_addr = (u8 __iomem *)pf->hw.hw_addr;
> 
>                 struct ice_vsi *vsi = ice_get_main_vsi(pf);
> 		cdev_info->vport_id = vsi->vsi_num;
> 		cdev_info->netdev = vsi->netdev;
> 		cdev_info->msix_count = pf->num_rdma_msix;
> 		cdev_info->msix_entries = &pf->msix_entries[pf-
> >rdma_base_vector];
> 
> 		ice_setup_dcb_qos_info(pf, cdev_info->qos_info);
> 
> Since the main place this cdev_info appears is in the ops API between the two
> modules, it looks to me like this is being designed in this obfuscated way to try
> and create a stable ABI between two modules.
> 
> Remove all the stable module ABI hackery before you resend it.
> 

I don't follow what the hackery is. Just because we use cdev_info in the .ops callbacks as opposed to ice_pf?

This is a private interface for Intel RDMA/PCI drivers and yes it is designed to be forward
looking especially since when we have near-term plans to use it.

Can you explain what you mean by stable module ABI hackery?

Shiraz