From: Dario Binacchi <dario.binacchi@xxxxxxxxxxxxxxxxxxxx>
Add initial documentation for Flexcan driver.
Signed-off-by: Dario Binacchi <dario.binacchi@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
---
.../device_drivers/can/freescale/flexcan.rst | 54 +++++++++++++++++++
.../networking/device_drivers/can/index.rst | 2 +
2 files changed, 56 insertions(+)
create mode 100644 Documentation/networking/device_drivers/can/freescale/flexcan.rst
diff --git a/Documentation/networking/device_drivers/can/freescale/flexcan.rst b/Documentation/networking/device_drivers/can/freescale/flexcan.rst
new file mode 100644
index 000000000000..8cc0359a8588
--- /dev/null
+++ b/Documentation/networking/device_drivers/can/freescale/flexcan.rst
@@ -0,0 +1,54 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+=============================
+Flexcan CAN Controller driver
+=============================
+
+Authors: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>,
+Dario Binacchi <dario.binacchi@xxxxxxxxxxxxxxxxxxxxx>
+
+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 reception of 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
+core 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
diff --git a/Documentation/networking/device_drivers/can/index.rst b/Documentation/networking/device_drivers/can/index.rst
index 218276818968..58b6e0ad3030 100644
--- a/Documentation/networking/device_drivers/can/index.rst
+++ b/Documentation/networking/device_drivers/can/index.rst
@@ -10,6 +10,8 @@ Contents:
.. toctree::
:maxdepth: 2
+ freescale/flexcan
+
.. only:: subproject and html
Indices
--
2.34.1
