Re: [PATCH net-next RFC 00/13] Add devlink reload level option

[Vasundhara Volam <vasundhara-v.volam@broadcom.com>]

On Wed, Aug 5, 2020 at 12:02 PM Moshe Shemesh <moshe@mellanox.com> wrote:
>
>
> On 8/4/2020 1:13 PM, Vasundhara Volam wrote:
> > On Mon, Aug 3, 2020 at 7:23 PM Moshe Shemesh <moshe@mellanox.com> wrote:
> >>
> >> On 8/3/2020 3:47 PM, Vasundhara Volam wrote:
> >>> On Mon, Aug 3, 2020 at 5:47 PM Moshe Shemesh <moshe@mellanox.com> wrote:
> >>>> On 8/3/2020 1:24 PM, Vasundhara Volam wrote:
> >>>>> On Tue, Jul 28, 2020 at 10:13 PM Jacob Keller <jacob.e.keller@intel.com> wrote:
> >>>>>> On 7/27/2020 10:25 PM, Vasundhara Volam wrote:
> >>>>>>> On Mon, Jul 27, 2020 at 4:36 PM Moshe Shemesh <moshe@mellanox.com> wrote:
> >>>>>>>> Introduce new option on devlink reload API to enable the user to select the
> >>>>>>>> reload level required. Complete support for all levels in mlx5.
> >>>>>>>> The following reload levels are supported:
> >>>>>>>>      driver: Driver entities re-instantiation only.
> >>>>>>>>      fw_reset: Firmware reset and driver entities re-instantiation.
> >>>>>>> The Name is a little confusing. I think it should be renamed to
> >>>>>>> fw_live_reset (in which both firmware and driver entities are
> >>>>>>> re-instantiated).  For only fw_reset, the driver should not undergo
> >>>>>>> reset (it requires a driver reload for firmware to undergo reset).
> >>>>>>>
> >>>>>> So, I think the differentiation here is that "live_patch" doesn't reset
> >>>>>> anything.
> >>>>> This seems similar to flashing the firmware and does not reset anything.
> >>>> The live patch is activating fw change without reset.
> >>>>
> >>>> It is not suitable for any fw change but fw gaps which don't require reset.
> >>>>
> >>>> I can query the fw to check if the pending image change is suitable or
> >>>> require fw reset.
> >>> Okay.
> >>>>>>>>      fw_live_patch: Firmware live patching only.
> >>>>>>> This level is not clear. Is this similar to flashing??
> >>>>>>>
> >>>>>>> Also I have a basic query. The reload command is split into
> >>>>>>> reload_up/reload_down handlers (Please correct me if this behaviour is
> >>>>>>> changed with this patchset). What if the vendor specific driver does
> >>>>>>> not support up/down and needs only a single handler to fire a firmware
> >>>>>>> reset or firmware live reset command?
> >>>>>> In the "reload_down" handler, they would trigger the appropriate reset,
> >>>>>> and quiesce anything that needs to be done. Then on reload up, it would
> >>>>>> restore and bring up anything quiesced in the first stage.
> >>>>> Yes, I got the "reload_down" and "reload_up". Similar to the device
> >>>>> "remove" and "re-probe" respectively.
> >>>>>
> >>>>> But our requirement is a similar "ethtool reset" command, where
> >>>>> ethtool calls a single callback in driver and driver just sends a
> >>>>> firmware command for doing the reset. Once firmware receives the
> >>>>> command, it will initiate the reset of driver and firmware entities
> >>>>> asynchronously.
> >>>> It is similar to mlx5 case here for fw_reset. The driver triggers the fw
> >>>> command to reset and all PFs drivers gets events to handle and do
> >>>> re-initialization.  To fit it to the devlink reload_down and reload_up,
> >>>> I wait for the event handler to complete and it stops at driver unload
> >>>> to have the driver up by devlink reload_up. See patch 8 in this patchset.
> >>>>
> >>> Yes, I see reload_down is triggering the reset. In our driver, after
> >>> triggering the reset through a firmware command, reset is done in
> >>> another context as the driver initiates the reset only after receiving
> >>> an ASYNC event from the firmware.
> >>
> >> Same here.
> >>
> >>> Probably, we have to use reload_down() to send firmware command to
> >>> trigger reset and do nothing in reload_up.
> >> I had that in previous version, but its wrong to use devlink reload this
> >> way, so I added wait with timeout for the event handling to complete
> >> before unload_down function ends. See mlx5_fw_wait_fw_reset_done(). Also
> >> the event handler stops before load back to have that done by devlink
> >> reload_up.
> > But "devlink dev reload" will be invoked by the user only on a single
> > dev handler and all function drivers will be re-instantiated upon the
> > ASYNC event. reload_down and reload_up are invoked only the function
> > which the user invoked.
> >
> > Take an example of a 2-port (PF0 and PF1) adapter on a single host and
> > with some VFs loaded on the device. User invokes "devlink dev reload"
> > on PF0, ASYNC event is received on 2 PFs and VFs for reset. All the
> > function drivers will be re-instantiated including PF0.
> >
> > If we wait for some time in reload_down() of PF0 and then call load in
> > reload_up(), this code will be different from other function drivers.
>
>
> I see your point here, but the user run devlink reload command on one
> PF, in this case of fw-reset it will influence other PFs, but that's a
> result of the fw-reset, the user if asked for params change or namespace
> change that was for this PF.
Right, if any driver is implementing only fw-reset have to leave
reload_up as an empty function.

>
> >>>    And returning from reload
> >>> does not mean that reset is complete as it is done in another context
> >>> and the driver notifies the health reporter once the reset is
> >>> complete. devlink framework may have to allow drivers to implement
> >>> reload_down only to look more clean or call reload_up only if the
> >>> driver notifies the devlink once reset is completed from another
> >>> context. Please suggest.