linux-kernel - RE: [PATCH] can: flexcan: fix timeout when set small bitrate

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Date:   Thu, 31 Jan 2019 09:09:44 +0000
From:   Aisheng Dong <aisheng.dong@....com>
To:     Joakim Zhang <qiangqing.zhang@....com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>
CC:     "wg@...ndegger.com" <wg@...ndegger.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] can: flexcan: fix timeout when set small bitrate

> From: Joakim Zhang
> Sent: Thursday, January 31, 2019 4:49 PM
[...]
> > > Current we can meet timeout issue when setting a small bitrate like
> > > 10000 as follows:
> > > root@...6qdlsolo:~# ip link set can0 up type can bitrate 10000 A
> > > link change request failed with some changes committed already.
> > > Interface can0 may have been left with an inconsistent
> > > configuration, please check.
> > > RTNETLINK answers: Connection timed out
> >
> > Which SoC are you using? Which clock rate has the flexcan IP core?
> 
>   We tested on i.MX6 series boards and all met this issue. And ipg clock rate is
> 66MHZ, per clock rate is 30MHZ.
> 
> > > It is caused by calling of flexcan_chip_unfreeze() timeout.
> > >
> > > Originally the code is using usleep_range(10, 20) for unfreeze
> > > operation, but the patch (8badd65 can: flexcan: avoid calling
> > > usleep_range from interrupt context) changed it into udelay(10)
> > > which is only a half delay of before, there're also some other delay
> changes.
> > >
> > > After only changed unfreeze delay back to udelay(20), the issue is gone.
> > > So other timeout values are kept the same as 8badd65 changed.
> >
> > Can you change FLEXCAN_TIMEOUT_US instead?
> 
>   Of course, we can change FLEXCAN_TIMEOUT_US to 100, but this will
> extend the time of enable/disable/softreset.
> Which method do you think is better?
> 

That seems not a big deal for an error case.
So change FLEXCAN_TIMEOUT_US seems like a good suggestion to me.
You can cook a patch with commit message updated. No need keep my author name
as it's a different solution.

Regards
Dong Aisheng

> Best Regards,
> Joakim Zhang
> 
> > > Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> > > Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> > > ---
> > >  drivers/net/can/flexcan.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c
> > > index 2bca867bcfaa..1d3a9053bbeb 100644
> > > --- a/drivers/net/can/flexcan.c
> > > +++ b/drivers/net/can/flexcan.c
> > > @@ -530,7 +530,7 @@ static int flexcan_chip_unfreeze(struct
> > > flexcan_priv
> > *priv)
> > >  	priv->write(reg, &regs->mcr);
> > >
> > >  	while (timeout-- && (priv->read(&regs->mcr) &
> FLEXCAN_MCR_FRZ_ACK))
> > > -		udelay(10);
> > > +		udelay(20);
> > >
> > >  	if (priv->read(&regs->mcr) & FLEXCAN_MCR_FRZ_ACK)
> > >  		return -ETIMEDOUT;
> > >
> >
> > 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   |