Re: [PATCH v4 18/23] ethdev: Helper to map to struct rte_pci_device

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-12-23 11:27, Jan Blunck:
> On Fri, Dec 23, 2016 at 9:30 AM, Thomas Monjalon
> <thomas.monjalon@6wind.com> wrote:
> > 2016-12-22 19:13, Jan Blunck:
> >> On Thu, Dec 22, 2016 at 4:21 PM, Thomas Monjalon
> >> <thomas.monjalon@6wind.com> wrote:
> >> > 2016-12-21 16:09, Jan Blunck:
> >> >> PCI drivers could use this helper instead of directly accessing fields of
> >> >> rte_eth_dev to map to rte_pci_device.
> >> > [...]
> >> >> +/**
> >> >> + * @internal
> >> >> + * Helper for drivers that need to convert from rte_eth_dev to rte_pci_device.
> >> >> + */
> >> >> +static inline struct rte_pci_device *__attribute__((always_inline))
> >> >> +rte_eth_dev_to_pci(struct rte_eth_dev *eth_dev)
> >> >> +{
> >> >> +     return eth_dev->pci_dev;
> >> >> +}
> >> >
> >> > Why adding this function instead of just using DEV_PCI_DEV(eth_dev->device)?
> >> >
> >> > I think we must try to avoid any PCI (or other bus) reference inside ethdev.h.
> >>
> >> David requested to move it from rte_pci.h to rte_ethdev.h.
> >>
> >> It could get forward declared here if one doesn't use it. On the other
> >> hand the rte_pci.h would be required to include rte_ethdev.h if we
> >> move it.
> >
> > I think there is a misunderstanding.
> > I was just suggesting to drop this function.
> 
> But that would undo the whole purpose of adding a helper. The purpose
> of the helper is to map from ethdev to the low-level rte_pci_device.
> If we remove this helper all users still need to know how to map to
> the embedded device structure. What you ask for also means that the
> patch "ethdev: Decouple struct rte_eth_dev from struct rte_pci_device"
> needs to change all users of the DEV_PCI_DEV() instead of changing the
> helper introduced in this patch.

Yes, using RTE_PCI_DEV(eth_dev->device) instead of rte_eth_dev_to_pci(eth_dev).
Is it a problem to know that the field name is "device" to access the
underlying device characteristics?

> Let me summarize the workable options from my perspective:
> 1. helper macro to map from eth_dev to pci_dev in rte_pci.h
> 2. helper inline function to map from eth_dev to pci_dev in rte_ethdev.h
> 3. put helpers into new header file rte_ethdrv.h
> 
> I'm still in favor of the first option but David suggested to remove
> it from eal. I could also counter the type-safety argument from
> Stephen by adding a type check to it.

My proposal is:
4. no helper, use eth_dev->device