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Date:   Wed, 12 Aug 2020 15:04:31 +0530
From:   Vasundhara Volam <vasundhara-v.volam@...adcom.com>
To:     Moshe Shemesh <moshe@...lanox.com>
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>,
        Netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next RFC 00/13] Add devlink reload level option

On Wed, Aug 5, 2020 at 1:51 PM Moshe Shemesh <moshe@...lanox.com> wrote:
>
>
> On 8/5/2020 9:55 AM, Vasundhara Volam wrote:
> > On Wed, Aug 5, 2020 at 12:02 PM Moshe Shemesh <moshe@...lanox.com> wrote:
> >>
> >> On 8/4/2020 1:13 PM, Vasundhara Volam wrote:
> >>> On Mon, Aug 3, 2020 at 7:23 PM Moshe Shemesh <moshe@...lanox.com> wrote:
> >>>> On 8/3/2020 3:47 PM, Vasundhara Volam wrote:
> >>>>> On Mon, Aug 3, 2020 at 5:47 PM Moshe Shemesh <moshe@...lanox.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@...el.com> wrote:
> >>>>>>>> On 7/27/2020 10:25 PM, Vasundhara Volam wrote:
> >>>>>>>>> On Mon, Jul 27, 2020 at 4:36 PM Moshe Shemesh <moshe@...lanox.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.
>
>
> No, its not only up the driver. The netns option is implemented by
> devlink and its running between reload_down and reload_up.
What I mean is, driver will provide a reload_up handler but it will
not do anything and simply return 0.
>
> >>>>>     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.

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