linux-kernel - Re: [EXT] Re: [PATCH] can: dev: clean up CAN ctrlmode when close CAN device

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Message-ID: <ad4c0921-3275-b466-95b4-a63944d5b71f@pengutronix.de>
Date:   Wed, 10 Apr 2019 19:49:45 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Joakim Zhang <qiangqing.zhang@....com>,
        "wg@...ndegger.com" <wg@...ndegger.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Cc:     dl-linux-imx <linux-imx@....com>,
        "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: [EXT] Re: [PATCH] can: dev: clean up CAN ctrlmode when close CAN
 device

On 4/10/19 9:55 AM, Joakim Zhang wrote:
> 
>> -----Original Message-----
>> From: Marc Kleine-Budde <mkl@...gutronix.de>
>> Sent: 2019年4月10日 15:19
>> To: Joakim Zhang <qiangqing.zhang@....com>; wg@...ndegger.com;
>> davem@...emloft.net
>> Cc: dl-linux-imx <linux-imx@....com>; linux-can@...r.kernel.org;
>> netdev@...r.kernel.org; linux-kernel@...r.kernel.org
>> Subject: [EXT] Re: [PATCH] can: dev: clean up CAN ctrlmode when close CAN
>> device
>>
>> On 4/10/19 8:27 AM, Joakim Zhang wrote:
>>> CAN driver always writes registers according to "ctrlmode", and now
>>> CAN framework will keep CAN ctrlmode after device closed.
>>>
>>> e.g. with following sequences:
>>> 1)ip link set can0 type can bitrate 1000000 loopback on 2)ip link set
>>> can0 up 3)ip link set can0 down 4)ip link set can0 type can bitrate
>>> 1000000 5)ip link set can0 up
>>>
>>> After this sequence, we may want to test loopback for the first time
>>> and not to test loopback second time. However, CAN device still keep
>>> "ctrlmode" as loopback on.
>>
>> Then you should configure loopback off in userspace.
> 
>  Got it. Thank you.
> 
>>> This patch intends to clean up CAN ctrlmode when close CAN device. We
>>> can set which ctrlmode we need when open CAN device again.
>>
>> Consider a CANFD device, where CANFD has been enabled. It will feel very
>> weird if the interface looses the CANFD property by just a ifdown; ifup.
> 
> Yes, you are right. But fd mode should compatible with normal can.

CANFD was just an example. Take CAN_CTRLMODE_ONE_SHOT as another
example. You don't want your network device settings to vanish if you
switch the interface off and on again.

> When I want to switch to normal can from fd mode. You mean that we
> should configure fd off in userspace as we may write some specific
> registers only by fd mode?

Whatever mode you enable via user space use user space to disable them
again.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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