| .. SPDX-License-Identifier: GPL-2.0+ |
| |
| ============================= |
| Flexcan CAN Controller driver |
| ============================= |
| |
| Authors: Marc Kleine-Budde <mkl@pengutronix.de>, |
| Dario Binacchi <dario.binacchi@amarulasolutions.com> |
| |
| On/off RTR frames reception |
| =========================== |
| |
| For most flexcan IP cores the driver supports 2 RX modes: |
| |
| - FIFO |
| - mailbox |
| |
| The older flexcan cores (integrated into the i.MX25, i.MX28, i.MX35 |
| and i.MX53 SOCs) only receive RTR frames if the controller is |
| configured for RX-FIFO mode. |
| |
| The RX FIFO mode uses a hardware FIFO with a depth of 6 CAN frames, |
| while the mailbox mode uses a software FIFO with a depth of up to 62 |
| CAN frames. With the help of the bigger buffer, the mailbox mode |
| performs better under high system load situations. |
| |
| As reception of RTR frames is part of the CAN standard, all flexcan |
| cores come up in a mode where RTR reception is possible. |
| |
| With the "rx-rtr" private flag the ability to receive RTR frames can |
| be waived at the expense of losing the ability to receive RTR |
| messages. This trade off is beneficial in certain use cases. |
| |
| "rx-rtr" on |
| Receive RTR frames. (default) |
| |
| The CAN controller can and will receive RTR frames. |
| |
| On some IP cores the controller cannot receive RTR frames in the |
| more performant "RX mailbox" mode and will use "RX FIFO" mode |
| instead. |
| |
| "rx-rtr" off |
| |
| Waive ability to receive RTR frames. (not supported on all IP cores) |
| |
| This mode activates the "RX mailbox mode" for better performance, on |
| some IP cores RTR frames cannot be received anymore. |
| |
| The setting can only be changed if the interface is down:: |
| |
| ip link set dev can0 down |
| ethtool --set-priv-flags can0 rx-rtr {off|on} |
| ip link set dev can0 up |
