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Date:   Tue, 19 May 2020 10:44:59 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Vasundhara Volam <vasundhara-v.volam@...adcom.com>,
        davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/4] bnxt_en: Add new "enable_hot_fw_reset"
 generic devlink parameter

On Tue, 19 May 2020 07:24:00 +0200 Jiri Pirko wrote:
> Tue, May 19, 2020 at 01:43:09AM CEST, kuba@...nel.org wrote:
> >On Mon, 18 May 2020 13:01:52 +0200 Jiri Pirko wrote:  
> >> Mon, May 18, 2020 at 10:27:15AM CEST, vasundhara-v.volam@...adcom.com wrote:  
> >> >This patchset adds support for a "enable_hot_fw_reset" generic devlink
> >> >parameter and use it in bnxt_en driver.
> >> >
> >> >Also, firmware spec. is updated to 1.10.1.40.    
> >> 
> >> Hi.
> >> 
> >> We've been discussing this internally for some time.
> >> I don't like to use params for this purpose.
> >> We already have "devlink dev flash" and "devlink dev reload" commands.
> >> Combination of these two with appropriate attributes should provide what
> >> you want. The "param" you are introducing is related to either "flash"
> >> or "reload", so I don't think it is good to have separate param, when we
> >> can extend the command attributes.
> >> 
> >> How does flash&reload work for mlxsw now:
> >> 
> >> # devlink flash
> >> Now new version is pending, old FW is running
> >> # devlink reload
> >> Driver resets the device, new FW is loaded
> >> 
> >> I propose to extend reload like this:
> >> 
> >>  devlink dev reload DEV [ level { driver-default | fw-reset | driver-only | fw-live-patch } ]
> >>    driver-default - means one of following to, according to what is
> >>                     default for the driver
> >>    fw-reset - does FW reset and driver entities re-instantiation
> >>    driver-only - does driver entities re-instantiation only
> >>    fw-live-patch - does only FW live patching - no effect on kernel
> >> 
> >> Could be an enum or bitfield. Does not matter. The point is to use
> >> reload with attribute to achieve what user wants. In your usecase, user
> >> would do:
> >> 
> >> # devlink flash
> >> # devlink reload level fw-live-patch  
> >
> >Unfortunately for SmartNICs and MultiHost systems the reset may not be
> >initiated locally. I agree it'd be great to have a normal netlink knob  
> 
> I don't follow. Locally initiated or not, why what I suggested is not
> enough to cover that?

Hopefully clear now after Michael's explanation :)

> >for this instead of a param. But it has to be some form of a policy of
> >allowing the reset to happen, rather than an action/trigger kind of
> >thing.  
> 
> The "host" allows to reset himself by the "smartnic", right? For that, I
> can imagine a param. But that is not the case of this patchset.
> 
> >Also user space notification should be generated when reset happens,
> >IMO. devlink dev info contents will likely change after reset, if
> >nothing else.  
> 
> I agree.
> 
> >Plus this functionality will need proper documentation.  
> 
> Also agreed.
> 
> >FWIW - I am unconvinced that applications will be happy to experience
> >network black outs, rather than being fully killed and re-spawned. For
> >a micro-service worker shutdown + re-spawn should be bread and butter.
> >But we already have ionic doing this, so seems like vendors are
> >convinced otherwise, so a common interface is probably a good step.  
> 
> Hmm, not sure I follow what you mean by this para in context of this
> patchset. Could you please explain? Thanks!

I'm saying I'm dubious users will actually enable the async remote
reset.

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