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

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Date:   Thu, 11 Apr 2019 08:38:45 +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 4/11/19 3:16 AM, Joakim Zhang wrote:
>> Whatever mode you enable via user space use user space to disable them
>> again.
> 
> Thank you for your detailed explanation. But in flexcan driver, it
> just set register bit when mode on and do not clear register bit when
> mode off, e.g. loopback, listennoly, 3 samples....

Let's see:

> 	reg = priv->read(&regs->ctrl);

The ctrl reg is read

> 	reg &= ~(FLEXCAN_CTRL_PRESDIV(0xff) |
> 		 FLEXCAN_CTRL_RJW(0x3) |
> 		 FLEXCAN_CTRL_PSEG1(0x7) |
> 		 FLEXCAN_CTRL_PSEG2(0x7) |
> 		 FLEXCAN_CTRL_PROPSEG(0x7) |
> 		 FLEXCAN_CTRL_LPB |
> 		 FLEXCAN_CTRL_SMP |
> 		 FLEXCAN_CTRL_LOM);

....the loopback mode, 3 sample mode and listen only mode bits are
masked out....

> 	reg |= FLEXCAN_CTRL_PRESDIV(bt->brp - 1) |
> 		FLEXCAN_CTRL_PSEG1(bt->phase_seg1 - 1) |
> 		FLEXCAN_CTRL_PSEG2(bt->phase_seg2 - 1) |
> 		FLEXCAN_CTRL_RJW(bt->sjw - 1) |
> 		FLEXCAN_CTRL_PROPSEG(bt->prop_seg - 1);
> 
> 	if (priv->can.ctrlmode & CAN_CTRLMODE_LOOPBACK)
> 		reg |= FLEXCAN_CTRL_LPB;
> 	if (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
> 		reg |= FLEXCAN_CTRL_LOM;
> 	if (priv->can.ctrlmode & CAN_CTRLMODE_3_SAMPLES)
> 		reg |= FLEXCAN_CTRL_SMP;

...and the bits are set, if enabled by user space...

> 	netdev_dbg(dev, "writing ctrl=0x%08x\n", reg);
> 	priv->write(reg, &regs->ctrl);

...and written to the register.

So all three bits will be unset, if unset by user space, right?

> When we configure mode off after configured mode on in the user
> space, corresponding bit will not change. Is this should be improved
> in flexcan driver?

That should work. If it doesn't work, we need a fix.

regards,
Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |



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