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Message-ID: <20240325205401.GF403975@kernel.org>
Date: Mon, 25 Mar 2024 20:54:01 +0000
From: Simon Horman <horms@...nel.org>
To: thomas.perrot@...tlin.com
Cc: Nicolas Ferre <nicolas.ferre@...rochip.com>,
Claudiu Beznea <claudiu.beznea@...on.dev>,
"David S . Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: macb: allow MTU change when the interface
is up
On Mon, Mar 25, 2024 at 04:27:35PM +0100, thomas.perrot@...tlin.com wrote:
> From: Thomas Perrot <thomas.perrot@...tlin.com>
>
> The macb_change_mtu callback doesn't allow MTU changes when the
> interface is up because the MTU is used to set the buffer size on
> GEM.
>
> So, to be able to change the MTU from userspace it is necessary to
> explicitly down then to up the interface, which is problematic in
> some cases.
>
> Then we suggest to reset the interface when the interface is already
> up to allow to change the MTU, regardless of if the interface is up
> or not.
>
> Signed-off-by: Thomas Perrot <thomas.perrot@...tlin.com>
Hi Thomas,
I'm not sure that it is expected behaviour for an interface
to reset like this when a change of MTU is requested.
While conversely I think it is common (if not entirely desirable)
to prohibit changing the MTU when an interface is up.
What is the problem being addressed here?
> ---
> drivers/net/ethernet/cadence/macb_main.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 898debfd4db3..5c20b162c5da 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -3019,11 +3019,19 @@ static int macb_close(struct net_device *dev)
>
> static int macb_change_mtu(struct net_device *dev, int new_mtu)
> {
> - if (netif_running(dev))
> - return -EBUSY;
> + int reset = 0;
nit: reset could be bool and set to true and false.
> +
> + /* On GEM the buffer size is based on the MTU */
> + if (netif_running(dev)) {
> + macb_close(dev);
> + reset = 1;
> + }
>
> dev->mtu = new_mtu;
>
> + if (reset)
> + macb_open(dev);
> +
> return 0;
> }
>
> --
> 2.44.0
>
>
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