On Wed. 16 Jun 2021 at 18:54, Marc Kleine-Budde [off-list ref] wrote:

On 24.02.2021 09:20:04, Vincent Mailhol wrote:

quoted

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

Signed-off-by: Vincent Mailhol <redacted>
---
 include/linux/can/bittiming.h | 65 +++++++++++++++++++++++++++++++++++
 include/linux/can/dev.h       |  3 ++
 2 files changed, 68 insertions(+)

diff --git a/include/linux/can/bittiming.h b/include/linux/can/bittiming.h
index 707575c668f4..91bf9f8926a7 100644
--- a/include/linux/can/bittiming.h
+++ b/include/linux/can/bittiming.h

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /* Copyright (c) 2020 Pengutronix, Marc Kleine-Budde <kernel@pengutronix.de>
+ * Copyright (c) 2021 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */

 #ifndef _CAN_BITTIMING_H

@@ -10,6 +11,70 @@

 #define CAN_SYNC_SEG 1

+/*
+ * struct can_tdc - CAN FD Transmission Delay Compensation parameters
+ *
+ * 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.
+ *
+ * To solve this issue, ISO 11898-1 introduces in section 11.3.3
+ * "Transmitter delay compensation" a SSP (Secondary Sample Point)
+ * equal to the distance, in time quanta, from the start of the bit
+ * time on the TX pin to the actual measurement on the RX pin.
+ *
+ * This structure contains the parameters to calculate that SSP.
+ *
+ * @tdcv: Transmitter Delay Compensation Value. Distance, in time
+ *   quanta, from when the bit is sent on the TX pin to when it is
+ *   received on the RX pin of the transmitter. Possible options:
+ *
+ *     O: automatic mode. The controller dynamically measure @tdcv

          ^

I think this is supposed to be a 0, not a O?
I'll send a patch

Absolutely. I am not sure how I did such a mistake. I was
probably not fully awake as there are two other grammar issues
there. I sent another patch to fix those.

Yours sincerely,
Vincent