can: add new CAN FD bittiming parameters: Transmitter Delay Compensation (TDC)

At high bit rates, the propagation delay from the TX pin to the RX pin
of the transceiver causes measurement errors: the sample point on the
RX pin might occur on the previous bit.

This issue is addressed in ISO 11898-1 section 11.3.3 "Transmitter
delay compensation" (TDC).

This patch adds two new structures: can_tdc and can_tdc_const in order
to implement this TDC.

The structures are then added to can_priv.

A controller supports TDC if an only if can_priv::tdc_const is not
NULL.

TDC is active if and only if:
  - fd flag is on
  - can_priv::tdc.tdco is not zero.
It is the driver responsibility to check those two conditions are met.

No new controller modes are introduced (i.e. no CAN_CTRL_MODE_TDC) in
order not to be redundant with above logic.

The names of the parameters are chosen to match existing CAN
controllers specification. References:
  - Bosch C_CAN FD8:
https://www.bosch-semiconductors.com/media/ip_modules/pdf_2/c_can_fd8/users_manual_c_can_fd8_r210_1.pdf
  - Microchip CAN FD Controller Module:
http://ww1.microchip.com/downloads/en/DeviceDoc/MCP251XXFD-CAN-FD-Controller-Module-Family-Reference-Manual-20005678B.pdf
  - SAM E701/S70/V70/V71 Family:
https://www.mouser.com/datasheet/2/268/60001527A-1284321.pdf

Link: https://lore.kernel.org/r/20210224002008.4158-2-mailhol.vincent@wanadoo.fr
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index ac4d83a1ab81..4795da0eb949 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -42,6 +42,9 @@ struct can_priv {
 	struct can_bittiming bittiming, data_bittiming;
 	const struct can_bittiming_const *bittiming_const,
 		*data_bittiming_const;
+	struct can_tdc tdc;
+	const struct can_tdc_const *tdc_const;
+
 	const u16 *termination_const;
 	unsigned int termination_const_cnt;
 	u16 termination;