RE: [PATCH 1/3] ixgbe: make link update thread periodic

[Jeff Daly <jeffd@silicom-usa.com>]

> -----Original Message-----
> From: Zhang, Qi Z <qi.z.zhang@intel.com>
> Sent: Sunday, May 29, 2022 7:25 PM
> To: Jeff Daly <jeffd@silicom-usa.com>; dev@dpdk.org; Yang, Qiming
> <qiming.yang@intel.com>; Wu, Wenjun1 <wenjun1.wu@intel.com>
> Cc: Stephen Douthit <stephend@silicom-usa.com>
> Subject: RE: [PATCH 1/3] ixgbe: make link update thread periodic
> 
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> 
> > -----Original Message-----
> > From: Jeff Daly <jeffd@silicom-usa.com>
> > Sent: Friday, May 20, 2022 2:03 AM
> > To: dev@dpdk.org; Yang, Qiming <qiming.yang@intel.com>; Wu, Wenjun1
> > <wenjun1.wu@intel.com>
> > Cc: Stephen Douthit <stephend@silicom-usa.com>
> > Subject: [PATCH 1/3] ixgbe: make link update thread periodic
> >
> > Rather than run-to-completion, allow the link update thread to be
> periodic.
> > This will set the stage for properly handling hot-plugging.
> 
> Could you explain more about what's the hot-plugging issue with run-to-
> completion you try to fix?
> 

it doesn't work right when you have SFPs.  (at least not on our platform or on an
82599 dual SFP add-in card we have).  run-to-completion only works 1x.  if you
remove and plug in a different SFP it doesn't work.  This patch series should have
been taking in context with the original SFP hotplug patch but apparently since
I can't ever seem to get the patch submission threading to do what I mean perhaps
some context has gone missing.  the SFP hotplug fix has been in the queue since 
Dec 2021, has been reworked several times, has gone through a change in Intel
maintainership.  this patch series makes the SFP hot plugging work like the Intel
kernel driver does.

> >
> > Signed-off-by: Jeff Daly <jeffd@silicom-usa.com>
> > Inspired-by: Stephen Douthit <stephend@silicom-usa.com>
> > ---
> >  drivers/net/ixgbe/base/ixgbe_common.c |   4 +-
> >  drivers/net/ixgbe/ixgbe_ethdev.c      | 180 ++++++++++----------------
> >  2 files changed, 71 insertions(+), 113 deletions(-)
> >
> > diff --git a/drivers/net/ixgbe/base/ixgbe_common.c
> > b/drivers/net/ixgbe/base/ixgbe_common.c
> > index aa843bd5c4a5..712062306491 100644
> > --- a/drivers/net/ixgbe/base/ixgbe_common.c
> > +++ b/drivers/net/ixgbe/base/ixgbe_common.c
> > @@ -4154,8 +4154,8 @@ s32 ixgbe_check_mac_link_generic(struct
> > ixgbe_hw *hw, ixgbe_link_speed *speed,
> >                       break;
> >               case ixgbe_mac_X550EM_x:
> >               case ixgbe_mac_X550EM_a:
> > -                     sfp_cage_full = IXGBE_READ_REG(hw, IXGBE_ESDP)
> > &
> > -                                     IXGBE_ESDP_SDP0;
> > +                     sfp_cage_full = !(IXGBE_READ_REG(hw, IXGBE_ESDP)
> > &
> > +                                       IXGBE_ESDP_SDP0);
> >                       break;
> >               default:
> >                       /* sanity check - No SFP+ devices here */ diff
> > --git
> 
> Looks like you change the behavior of link status check for x550.
> I'm not an ixgbe expert, but I know this is not kernel driver's
> implementation.
> 

sigh.  this was supposed to be part of a different patch which also had some
question about functionality.  the SDP0 bit check doesn't specifically need to be
a check for a '1', since the bit reflects the state of the pin on the platform.  Intel's
platform implementations have an inverter on the board to switch the state.
MOD_ABS from an SFP will be '0' when an SFP is plugged in.  with an inverter in
the platform the signal will be '1' when an SFP is plugged in.  there's no guidance
from Intel's platform design guide that an inverter needs to be between the SFP
and the NIC SDP pin so having it only follow Intel's platform implementations is
hard to justify.  

> So do you think this is a fix for both DPDK and kernel driver?  if it is, please
> move this change into a  separate patch and we need to reach the right
> expert to approve this.
> 
> 

no, as explained above.