linux-kernel - Re: [PATCH net-next] can: dev: call netif_carrier_off() in register

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Message-ID: <ff8160d4-3357-9b4f-1840-bbe46195da5a@prevas.dk>
Date:   Wed, 26 Jun 2019 09:31:39 +0000
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC:     Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Rasmus Villemoes <Rasmus.Villemoes@...vas.se>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] can: dev: call netif_carrier_off() in
 register_candev()

On 24/06/2019 19.26, Willem de Bruijn wrote:
> On Mon, Jun 24, 2019 at 4:34 AM Rasmus Villemoes
> <rasmus.villemoes@...vas.dk> wrote:
>>
>> CONFIG_CAN_LEDS is deprecated. When trying to use the generic netdev
>> trigger as suggested, there's a small inconsistency with the link
>> property: The LED is on initially, stays on when the device is brought
>> up, and then turns off (as expected) when the device is brought down.
>>
>> Make sure the LED always reflects the state of the CAN device.
>>
>> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
> 
> Should this target net?

No, I think this should go through the CAN tree. Perhaps I've
misunderstood when to use the net-next prefix - is that only for things
that should be applied directly to the net-next tree? If so, sorry.

> Regardless of CONFIG_CAN_LEDS deprecation,
> this is already not initialized properly if that CONFIG is disabled
> and a can_led_event call at device probe is a noop.

I'm not sure I understand this part. The CONFIG_CAN_LEDS support for
showing the state of the interface is implemented via hooking into the
ndo_open/ndo_stop callbacks, and does not look at or touch the
__LINK_STATE_NOCARRIER bit at all.

Other than via the netdev LED trigger I don't think one can even observe
the slightly odd initial state of the __LINK_STATE_NOCARRIER bit for CAN
devices, which is why I framed this as a fix purely to allow the netdev
trigger to be a closer drop-in replacement for CONFIG_CAN_LEDS.

Rasmus