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

From: Oliver Hartkopp
Date: Tue Jun 30 2020 - 12:18:13 EST




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@xxxxxxxx>
Sent: 2020å6æ30æ 2:18
To: linux-can@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx
Cc: Wolfgang Grandegger <wg@xxxxxxxxxxxxxx>; Marc Kleine-Budde
<mkl@xxxxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Jakub
Kicinski <kuba@xxxxxxxxxx>; Joakim Zhang <qiangqing.zhang@xxxxxxx>;
dl-linux-imx <linux-imx@xxxxxxx>; Michael Walle <michael@xxxxxxxx>
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@xxxxxxxx>
---
Âdrivers/net/can/flexcan.c | 19 ++++++++++++++++---
Â1 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 @@
Â#define FLEXCAN_CTRL2_MRPÂÂÂÂÂÂÂ BIT(18)
Â#define FLEXCAN_CTRL2_RRSÂÂÂÂÂÂÂ BIT(17)
Â#define FLEXCAN_CTRL2_EACENÂÂÂÂÂÂÂ BIT(16)
+#define FLEXCAN_CTRL2_ISOCANFDENÂÂÂ BIT(12)

Â/* FLEXCAN memory error control register (MECR) bits */
Â#define FLEXCAN_MECR_ECRWRDISÂÂÂÂÂÂÂ BIT(31)
@@ -1344,14 +1345,25 @@ static int flexcan_chip_start(struct net_device
*dev)
ÂÂÂÂ else
ÂÂÂÂÂÂÂÂ reg_mcr |= FLEXCAN_MCR_SRX_DIS;

-ÂÂÂ /* MCR - CAN-FD */
-ÂÂÂ if (priv->can.ctrlmode & CAN_CTRLMODE_FD)
+ÂÂÂ /* MCR, CTRL2
+ÂÂÂÂ *
+ÂÂÂÂ * CAN-FD mode
+ÂÂÂÂ * ISO CAN-FD mode
+ÂÂÂÂ */
+ÂÂÂ reg_ctrl2 = priv->read(&regs->ctrl2);
+ÂÂÂ if (priv->can.ctrlmode & CAN_CTRLMODE_FD) {
ÂÂÂÂÂÂÂÂ reg_mcr |= FLEXCAN_MCR_FDEN;
-ÂÂÂ else
+ÂÂÂÂÂÂÂ reg_ctrl2 |= FLEXCAN_CTRL2_ISOCANFDEN;
+ÂÂÂ } else {
ÂÂÂÂÂÂÂÂ reg_mcr &= ~FLEXCAN_MCR_FDEN;
+ÂÂÂ }
+
+ÂÂÂ if (priv->can.ctrlmode & CAN_CTRLMODE_FD_NON_ISO)
+ÂÂÂÂÂÂÂ 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 \
ÂÂ 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))
ÂÂÂÂÂÂÂÂÂ 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