Re: [PATCH v2 net-next 1/4] devlink: Add new "allow_fw_live_reset" generic device parameter.

From: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Netdev <netdev@vger.kernel.org>,
	Michael Chan <michael.chan@broadcom.com>,
	Jiri Pirko <jiri@resnulli.us>, David Miller <davem@davemloft.net>,
	Jiri Pirko <jiri@mellanox.com>
Subject: Re: [PATCH v2 net-next 1/4] devlink: Add new "allow_fw_live_reset" generic device parameter.
Date: Fri, 29 May 2020 19:59:45 +0530	[thread overview]
Message-ID: <CAACQVJoi-KKxxWZxoRx-tyn=88TWxA5D_dqcW0yEG+4GDEj6pw@mail.gmail.com> (raw)
In-Reply-To: <20200528120551.689251bf@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>

On Fri, May 29, 2020 at 12:35 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Thu, 28 May 2020 07:20:00 +0530 Vasundhara Volam wrote:
> > > > The permanent value should be the NVRAM value.  If the NVRAM value is
> > > > false, the feature is always and unconditionally disabled.  If the
> > > > permanent value is true, the feature will only be available when all
> > > > loaded drivers indicate support for it and set the runtime value to
> > > > true.  If an old driver is loaded afterwards, it wouldn't indicate
> > > > support for this feature and it wouldn't set the runtime value to
> > > > true.  So the feature will not be available until the old driver is
> > > > unloaded or upgraded.
> > >
> > > Setting this permanent value to false makes the FW's life easier?
> >
> > It just disables the feature.
> >
> > > Otherwise why not always have it enabled and just depend on hosts
> > > not opting in?
> >
> > We are providing permanent value as a flexibility to user. We can
> > remove it, if it makes things easy and clear.
>
> I'd think less knobs means less to understand for the user and less
> to test for the vendor. If disabling the feature doesn't buy FW
> anything then perhaps it can just serve the purpose of setting the
> default?
>
> > > > > > 3. Now enable the capability in the device and reboot for device to
> > > > > > enable the capability. Firmware does not get reset just by setting the
> > > > > > param to true.
> > > > > >
> > > > > > $ devlink dev param set pci/0000:3b:00.1 name allow_fw_live_reset
> > > > > > value true cmode permanent
> > > > > >
> > > > > > 4. After reboot, values of param.
> > > > >
> > > > > Is the reboot required here?
> > > >
> > > > In general, our new NVRAM permanent parameters will take effect after
> > > > reset (or reboot).
> > > >
> > > > > > $ devlink dev param show pci/0000:3b:00.1 name allow_fw_live_reset
> > > > > > pci/0000:3b:00.1:
> > > > > >   name allow_fw_live_reset type generic
> > > > > >     values:
> > > > > >       cmode runtime value true
> > > > >
> > > > > Why is runtime value true now?
> > > > >
> > > >
> > > > If the permanent (NVRAM) parameter is true, all loaded new drivers
> > > > will indicate support for this feature and set the runtime value to
> > > > true by default.  The runtime value would not be true if any loaded
> > > > driver is too old or has set the runtime value to false.
> > >
> > > Okay, the parameter has a bit of a dual role as it controls whether the
> > > feature is available (false -> true transition requiring a reset/reboot)
> > > and the default setting of the runtime parameter. Let's document that
> > > more clearly.
> > Please look at the 3/4 patch for more documentation in the bnxt.rst
> > file. We can add more documentation, if needed, in the bnxt.rst file.
>
> Ack, I read that, but it wasn't nearly clear enough. The command
> examples helped much more.  I think the doc should be expanded.
Thank you for looking into it. I will soon send out the next version
of patchset with expanded documentation and param is split into two
with better renaming.

Thanks.