Hi Marc, > -----Original Message----- > From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> > Sent: 2019年1月31日 17:12 > To: Joakim Zhang <qiangqing.zhang@xxxxxxx>; linux-can@xxxxxxxxxxxxxxx > Cc: wg@xxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>; Aisheng > Dong <aisheng.dong@xxxxxxx> > Subject: Re: [PATCH] can: flexcan: fix timeout when set small bitrate > > On 1/31/19 9:48 AM, Joakim Zhang wrote: > >> 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. > > ok > > > > >>> 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? > > If you double to FLEXCAN_TIMEOUT_US to 100, the loops in question will spin > at maximum the double time. But the loops are left as soon as the condition is > satisfied. > > It will fix your problem with the 10 kbit/s bitrate. But if there is some kind of > problem with the IP core it will still fail, it just takes double amount of time > (100 µs + overhead) until the function returns. > > I don't see any harm in looping longer: > - The previous good case is unchanged. > - The error case takes double amount of time. > - Your problem is hopefully fixed. Thanks for your explanation, I will cook a patch then resend. Best Regards, Joakim Zhang > 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 |
