netdev - Re: [PATCH] ravb: implement MTU change while device is up

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Date:   Thu, 23 May 2019 03:02:45 +0200 (CEST)
From:   Ulrich Hecht <uli@...nd.eu>
To:     Simon Horman <horms@...ge.net.au>, Wolfram Sang <wsa@...-dreams.de>
Cc:     Niklas Söderlund <niklas.soderlund@...natech.se>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org,
        davem@...emloft.net, magnus.damm@...il.com
Subject: Re: [PATCH] ravb: implement MTU change while device is up


> On May 22, 2019 at 1:59 PM Simon Horman <horms@...ge.net.au> wrote:
> 
> 
> On Mon, May 20, 2019 at 02:09:54PM +0200, Wolfram Sang wrote:
> > 
> > > > > > > >    How about the code below instead?
> > > > > > > > 
> > > > > > > > 	if (netif_running(ndev))
> > > > > > > > 		ravb_close(ndev);
> > > > > > > > 
> > > > > > > >  	ndev->mtu = new_mtu;
> > > > > > > > 	netdev_update_features(ndev);
> > > > > > > 
> > > > > > > Is there a need to call netdev_update_features() even if the if is not 
> > > > > > > running?
> > > > > > 
> > > > > > In my testing, it didn't seem so.
> > > > > 
> > > > > That may be because your testing doesn't cover cases where it would make
> > > > > any difference.
> > > > 
> > > > Cases other than changing the MTU while the device is up?
> > > 
> > > I was thinking of cases where listeners are registered for the
> > > notifier that netdev_update_features() triggers.
> > 
> > Where are we here? Is this a blocker?
> 
> I don't think this is a blocker but I would lean towards leaving
> netdev_update_features() in unless we are certain its not needed.
>

I have read through the code and have indeed not found any indication that netdev_update_features() or something equivalent is called implicitly when the device is closed and reopened. I'll send a v2.

CU
Uli