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docs: networking: device drivers: can: add flexcan
Add initial documentation for Flexcan driver.
Link: https://lore.kernel.org/all/20220107193105.1699523-8-mkl@pengutronix.de
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
authored by
Dario Binacchi
and committed by
Marc Kleine-Budde
bc3897f7
32db1660
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Documentation/networking/device_drivers/can/freescale/flexcan.rst
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Documentation/networking/device_drivers/can/freescale/flexcan.rst
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.. SPDX-License-Identifier: GPL-2.0+
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=============================
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Flexcan CAN Controller driver
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=============================
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Authors: Marc Kleine-Budde <mkl@pengutronix.de>,
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Dario Binacchi <dario.binacchi@amarula.solutions.com>
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On/off RTR frames reception
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===========================
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For most flexcan IP cores the driver supports 2 RX modes:
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- FIFO
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- mailbox
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The older flexcan cores (integrated into the i.MX25, i.MX28, i.MX35
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and i.MX53 SOCs) only receive RTR frames if the controller is
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configured for RX-FIFO mode.
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The RX FIFO mode uses a hardware FIFO with a depth of 6 CAN frames,
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while the mailbox mode uses a software FIFO with a depth of up to 62
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CAN frames. With the help of the bigger buffer, the mailbox mode
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performs better under high system load situations.
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As reception of RTR frames is part of the CAN standard, all flexcan
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cores come up in a mode where RTR reception is possible.
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With the "rx-rtr" private flag the ability to receive RTR frames can
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be waived at the expense of losing the ability to receive RTR
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messages. This trade off is beneficial in certain use cases.
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"rx-rtr" on
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Receive RTR frames. (default)
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The CAN controller can and will receive RTR frames.
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On some IP cores the controller cannot receive RTR frames in the
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more performant "RX mailbox" mode and will use "RX FIFO" mode
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instead.
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"rx-rtr" off
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Waive ability to receive RTR frames. (not supported on all IP cores)
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This mode activates the "RX mailbox mode" for better performance, on
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some IP cores RTR frames cannot be received anymore.
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The setting can only be changed if the interface is down::
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ip link set dev can0 down
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ethtool --set-priv-flags can0 rx-rtr {off|on}
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ip link set dev can0 up