Re: [dpdk-dev] [PATCH v5 00/15] common ethdev linkstatus functions

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 17 Jan 2018 14:32:17 +0000
Ferruh Yigit <ferruh.yigit@intel.com> wrote:

> On 1/17/2018 7:56 AM, Andrew Rybchenko wrote:
> > On 01/16/2018 09:37 PM, Stephen Hemminger wrote:  
> >> While reviewing drivers, noticed a lot of unnecessary
> >> duplication of code in drivers for handling the eth_dev link status
> >> information. While consolidating this, it also became obvious that
> >> some drivers behave differently for no good reason.
> >>
> >> It also was a good chance to introduce atomic exchange primitives
> >> in EAL because there are other places using cmpset where not
> >> necessary (such as bonding).
> >>
> >> Mostly only compile tested only, don't have all of the hardware
> >> available (except ixgbe and virtio) to test.
> >>
> >> Note: the eth_dev_link_update function return value is inconsistent
> >> across drivers. Should be changed to be void.  
> > 
> > I would say "link_update" callback return value is inconsistent across
> > drivers. I'm not sure which direction is right here: make it consistent
> > or make it void. Also any changes in link information could be
> > important. As I understand it should not happen without up/down,
> > but bugs with loss of intermediate transitions are definitely possible.
> > So, notifying about any changes in link information is definitely safer.
> > May be not now.  
> 
> Again, why not return previous link status, it is simple enough to prevent
> inconsistent usage.
> 
> rte_eth_link_get() already discards the return value, so won't be a problem there.
> 
> For the cases PMD would like know about link changes, they will need to
> implement almost same link_update function with a return value, so why not use
> existing link_update function?
> 
> Like been in virtio, link_update() used in interrupt handler, and calls a
> callback process if status changes. When link_update() return status changed to
> void, I guess they will need to implement another version of the link_update
> with return and use it.

The interrupt and non-interrupt model are different.
Also the driver internally may want to do something different, this is about
the return value for dev_ops->link_update.  The code in rte_eth_dev never
used the return value. The bonding driver was expecting it to work but it
doesn't. Anyway drivers shouldn't in general be directly calling other
devices eth_dev_ops