linux-kernel - Re: [net-next] net: dsa: qca8k: only change the MIB_EN bit in MODULE

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Date:   Tue, 9 Nov 2021 01:38:16 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Robert Marko <robert.marko@...tura.hr>
Cc:     Andrew Lunn <andrew@...n.ch>, vivien.didelot@...il.com,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>, kuba@...nel.org,
        netdev@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Gabor Juhos <j4g8y7@...il.com>, John Crispin <john@...ozen.org>
Subject: Re: [net-next] net: dsa: qca8k: only change the MIB_EN bit in
 MODULE_EN register

On Mon, Nov 08, 2021 at 11:13:30PM +0100, Robert Marko wrote:
> > The driver keeps state. If the switch just resets by itself, what do you
> > think will continue to work fine afterwards? The code path needs testing.
> > I am not convinced that a desynchronized software state is any better
> > than a lockup.
> 
> It's really unpredictable, as QCA doesn't specify what does the software reset
> actually does, as I doubt that they are completely resetting the
> switch to HW defaults.
> But since I was not able to trigger the QM error and the resulting
> reset, it's hard to tell.
> Phylink would probably see the ports going down and trigger the MAC
> configuration again,
> this should at least allow using the ports and forwarding to CPU again.
> However, it may also reset the forwarding config to basically flooding
> all ports which is the default
> which is not great.
> 
> But I do agree that it may not be a lot better than a lockup.

I'm not sure what you expect going forward. You haven't proven an issue
with the actual code structure, or an improvement brought by your change.
Allowing the hardware to autonomously reconfigure itself, even if
partially, is out of the question (of course, that's if and only if I
understand correctly the info that you've presented).