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

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Message-ID: <CAACQVJpZZPfiWszZ36E0Awuo2Ad1w5=4C1rgG=d4qPiWVP609Q@mail.gmail.com>
Date:   Mon, 3 Aug 2020 18:17:33 +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 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.

Probably, we have to use reload_down() to send firmware command to
trigger reset and do nothing in reload_up. 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.