linux-kernel - Re: [PATCH 2/2] can: flexcan: add support for ISO CAN-FD

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Date:   Tue, 30 Jun 2020 18:15:01 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Michael Walle <michael@...le.cc>,
        Joakim Zhang <qiangqing.zhang@....com>
Cc:     linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH 2/2] can: flexcan: add support for ISO CAN-FD



On 30.06.20 07:53, Michael Walle wrote:
> [+ Oliver]
> 
> Hi Joakim,
> 
> Am 2020-06-30 04:42, schrieb Joakim Zhang:
>>> -----Original Message-----
>>> From: Michael Walle <michael@...le.cc>
>>> Sent: 2020年6月30日 2:18
>>> To: linux-can@...r.kernel.org; netdev@...r.kernel.org;
>>> linux-kernel@...r.kernel.org
>>> Cc: Wolfgang Grandegger <wg@...ndegger.com>; Marc Kleine-Budde
>>> <mkl@...gutronix.de>; David S . Miller <davem@...emloft.net>; Jakub
>>> Kicinski <kuba@...nel.org>; Joakim Zhang <qiangqing.zhang@....com>;
>>> dl-linux-imx <linux-imx@....com>; Michael Walle <michael@...le.cc>
>>> Subject: [PATCH 2/2] can: flexcan: add support for ISO CAN-FD
>>>
>>> Up until now, the controller used non-ISO CAN-FD mode, although it 
>>> supports it.
>>> Add support for ISO mode, too. By default the hardware is in non-ISO 
>>> mode and
>>> an enable bit has to be explicitly set.
>>>
>>> Signed-off-by: Michael Walle <michael@...le.cc>
>>> ---
>>>  drivers/net/can/flexcan.c | 19 ++++++++++++++++---
>>>  1 file changed, 16 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c index
>>> 183e094f8d66..a92d3cdf4195 100644
>>> --- a/drivers/net/can/flexcan.c
>>> +++ b/drivers/net/can/flexcan.c
>>> @@ -94,6 +94,7 @@
>>>  #define FLEXCAN_CTRL2_MRP        BIT(18)
>>>  #define FLEXCAN_CTRL2_RRS        BIT(17)
>>>  #define FLEXCAN_CTRL2_EACEN        BIT(16)
>>> +#define FLEXCAN_CTRL2_ISOCANFDEN    BIT(12)
>>>
>>>  /* FLEXCAN memory error control register (MECR) bits */
>>>  #define FLEXCAN_MECR_ECRWRDIS        BIT(31)
>>> @@ -1344,14 +1345,25 @@ static int flexcan_chip_start(struct net_device
>>> *dev)
>>>      else
>>>          reg_mcr |= FLEXCAN_MCR_SRX_DIS;
>>>
>>> -    /* MCR - CAN-FD */
>>> -    if (priv->can.ctrlmode & CAN_CTRLMODE_FD)
>>> +    /* MCR, CTRL2
>>> +     *
>>> +     * CAN-FD mode
>>> +     * ISO CAN-FD mode
>>> +     */
>>> +    reg_ctrl2 = priv->read(&regs->ctrl2);
>>> +    if (priv->can.ctrlmode & CAN_CTRLMODE_FD) {
>>>          reg_mcr |= FLEXCAN_MCR_FDEN;
>>> -    else
>>> +        reg_ctrl2 |= FLEXCAN_CTRL2_ISOCANFDEN;
>>> +    } else {
>>>          reg_mcr &= ~FLEXCAN_MCR_FDEN;
>>> +    }
>>> +
>>> +    if (priv->can.ctrlmode & CAN_CTRLMODE_FD_NON_ISO)
>>> +        reg_ctrl2 &= ~FLEXCAN_CTRL2_ISOCANFDEN;
>>
>>
> 
> [..]
>> ip link set can0 up type can bitrate 1000000 dbitrate 5000000 fd on
>> ip link set can0 up type can bitrate 1000000 dbitrate 5000000 fd on \
>>    fd-non-iso on
> 
> vs.
> 
>> ip link set can0 up type can bitrate 1000000 dbitrate 5000000 
>> fd-non-iso on
> 
> I haven't found anything if CAN_CTRLMODE_FD_NON_ISO depends on
> CAN_CTRLMODE_FD. I.e. wether CAN_CTRLMODE_FD_NON_ISO can only be set if
> CAN_CTRLMODE_FD is also set.
> 
> Only the following piece of code, which might be a hint that you
> have to set CAN_CTRLMODE_FD if you wan't to use CAN_CTRLMODE_FD_NON_ISO:
> 
> drivers/net/can/dev.c:
>    /* do not check for static fd-non-iso if 'fd' is disabled */
>    if (!(maskedflags & CAN_CTRLMODE_FD))
>            ctrlstatic &= ~CAN_CTRLMODE_FD_NON_ISO;
> 
> If CAN_CTRLMODE_FD_NON_ISO can be set without CAN_CTRLMODE_FD, what
> should be the mode if both are set at the same time?

CAN_CTRLMODE_FD_NON_ISO is only relevant when CAN_CTRLMODE_FD is set.

So in the example from above

ip link set can0 up type can bitrate 1000000 dbitrate 5000000 fd-non-iso on

either the setting of 'dbitrate 5000000' and 'fd-non-iso on' is pointless.

When switching to FD-mode with 'fd on' the FD relevant settings need to 
be applied.

FD ISO is the default.

Did this help or did I get anything wrong?

Best,
Oliver