netdev - Re: [PATCH] net-sysfs: allow changing sysfs carrier when interface is down

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Date:   Sun, 5 Jun 2022 20:50:29 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
Cc:     "kuba@...nel.org" <kuba@...nel.org>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] net-sysfs: allow changing sysfs carrier when interface
 is down

On Thu, Jun 02, 2022 at 06:01:08PM +0000, Joakim Tjernlund wrote:
> On Thu, 2022-06-02 at 10:52 -0700, Jakub Kicinski wrote:
> > On Thu, 2 Jun 2022 17:15:13 +0000 Joakim Tjernlund wrote:
> > > > What is "our HW", what kernel driver does it use and why can't the
> > > > kernel driver take care of making sure the device is not accessed
> > > > when it'd crash the system?  
> > > 
> > > It is a custom asic with some homegrown controller. The full config path is too complex for kernel too
> > > know and depends on user input.
> > 
> > We have a long standing tradition of not caring about user space
> > drivers in netdev land. I see no reason to merge this patch upstream.
> 
> This is not a user space driver. View it as a eth controller with a dum PHY
> which cannot convey link status. The kernel driver then needs help with managing carrier.

Please post the MAC driver then. We don't really like changes to the
kernel without a user. You MAC driver would be such a user.

Could you also tell us more about the PHY. What capabilities does it
have? I assume it is not C22 compatible. Does it at least have some
sort of indicator of link? What might make sense is to use the
fixed-link code. You can provide a callback which gives the actual
link status up/down. And the fixed-link driver looks like a real PHY,
so the MAC driver does not need to do anything special.

   Andrew