Hi Marc,
On Fri, Jan 7, 2022 at 8:31 PM Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> wrote:
>
> 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.
only receive RTR frames
> +
> +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.
all flexcan cores
Thanks and regards,
Dario
> +
> +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
>
>
--
Dario Binacchi
Embedded Linux Developer
dario.binacchi@xxxxxxxxxxxxxxxxxxxx
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