Re: [PATCH v4 1/3] lib/librte_ether: add support for port reset

["Zhao1, Wei" <wei.zhao1@intel.com>]

Hi, Thomas Monjalon

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Thursday, April 13, 2017 6:07 PM
> To: Zhao1, Wei <wei.zhao1@intel.com>
> Cc: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Mcnamara, John
> <john.mcnamara@intel.com>; dev@dpdk.org; Lu, Wenzhuo
> <wenzhuo.lu@intel.com>
> Subject: Re: [dpdk-dev] [PATCH v4 1/3] lib/librte_ether: add support for port
> reset
> 
> 2017-04-13 08:55, Zhao1, Wei:
> > From: Ananyev, Konstantin
> > > From: Zhao1, Wei
> > > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > > > 2017-04-06 02:57, Zhao1, Wei:
> > > > > > >   /**
> > > > > > > > + * Reset an ethernet device when it's not working. One
> > > > > > > > + scenario is, after PF
> > > > > > > > + * port is down and up, the related VF port should be reset.
> > > > > > > > + * The API will stop the port, clear the rx/tx queues,
> > > > > > > > + re-setup the rx/tx
> > > > > > > > + * queues, restart the port.
> > > > > > >
> > > > > > > s/The API/This function/
> > > > > > >
> > > > > > > Please explain exactly the responsibility of this function,
> > > > > > > and how it is different from calling stop/configure/start.
> > > > > >
> > > > > > In this reset feature, reset function can do the calling
> > > > > > stop/configure/start process, but also It can also do some
> > > > > > restore work for the port, for example, it can restore the
> > > > > > added parameters  of
> > > > > vlan,  mac_addrs, promisc_unicast_enabled falg and
> > > > > promisc_multicast_enabled flag.
> > >
> > > Ok, but why start/stop can't do these things?
> > > Konstantin
> >
> > This is because in i40e PMD code, start and stop process do not have
> > the process of store and restore the added key parameters. Not  only
> > i40e but also other PMD code. So, in the function pointed to by dev_reset,
> we add specific function do store and restore of some of the important
> parameters  listed above.
> 
> Why store and restore cannot be implemented in start/stop functions?

Because reset and  start/stop are used for two purposes,  for example:
Some user maybe just start/stop the port  and he do not care what key parameters
has been configuration last time, and even worse when he want to clear all the configuration last time ,
if we add specific function do store and restore in  that two function, it is useless for them,
and may cause a result that user do not expect.