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Date:   Thu, 11 Apr 2019 08:12:10 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>,
        "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


> -----Original Message-----
> From: Marc Kleine-Budde <mkl@...gutronix.de>
> Sent: 2019年4月11日 14:39
> 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: 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?

Oh, I see. Thank you!

Best Regards,
Joakim Zhang
> 
> > 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     |
> Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
> Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |

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