From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Oliver Hartkopp <socketcan@hartkopp.net>,
Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
linux-can@vger.kernel.org
Cc: kernel@pengutronix.de
Subject: Re: [net-rfc 04/16] can: dev: can_get_len(): add a helper function to get the correct length of Classical frames
Date: Tue, 20 Oct 2020 17:02:00 +0200 [thread overview]
Message-ID: <24c434cf-95c2-8936-387b-cb651c029781@pengutronix.de> (raw)
In-Reply-To: <6f869e47-9a76-3398-0b64-2d573d412f4c@hartkopp.net>
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On 10/20/20 2:38 PM, Oliver Hartkopp wrote:
[...]
> You can create a DLC of 13 for Classical CAN. And your CAN controller
> gets 8 bytes from it and says to the network layer: Here is a CAN frame
> with 8 bytes payload.
>
> Have you ever read out a CAN controller register and found a value
> greater than 8 on the register of the DLC value?
>
> I believe you didn't. The CAN controller sees the DLC but provides 8
> bytes as DLC=8.
I just checked on the flexcan (mx6) and the mcp2518fd. I hardcoded a TX-dlc of
12 in both drivers and printed the raw dlc value in the RX-path:
> Oct 20 16:46:08 riot kernel: flexcan_mailbox_read: dlc=12
> Oct 20 16:46:10 riot kernel: mcp251xfd_hw_rx_obj_to_skb: dlc=12
The userspace shows a consistent len=8.
If we want to support CAN-2.0 with DLC > 8, we have to audit the TX-path every
driver and remove the can_dropped_invalid_skb() check.
I'm not sure what to do about the RX, with breaking user space ABI.
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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next prev parent reply other threads:[~2020-10-20 15:02 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-19 19:05 [RFC]: can 2020-10-19 Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 01/16] can: proc: can_remove_proc(): silence remove_proc_entry warning Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 02/16] can: rx-offload: don't call kfree_skb() from IRQ context Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 03/16] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard " Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 04/16] can: dev: can_get_len(): add a helper function to get the correct length of Classical frames Marc Kleine-Budde
2020-10-19 20:35 ` Oliver Hartkopp
2020-10-20 6:35 ` Marc Kleine-Budde
2020-10-20 11:30 ` Vincent Mailhol
2020-10-20 11:48 ` Marc Kleine-Budde
2020-10-20 12:38 ` Oliver Hartkopp
2020-10-20 15:02 ` Marc Kleine-Budde [this message]
2020-10-20 16:07 ` Vincent Mailhol
2020-10-20 17:04 ` Oliver Hartkopp
2020-10-20 18:50 ` Marc Kleine-Budde
2020-10-21 0:52 ` Vincent Mailhol
2020-10-21 6:23 ` Vincent MAILHOL
2020-10-21 7:11 ` Joakim Zhang
2020-10-21 7:21 ` Marc Kleine-Budde
2020-10-21 7:48 ` Joakim Zhang
2020-10-21 9:21 ` Oliver Hartkopp
2020-10-21 9:48 ` Oliver Hartkopp
2020-10-21 11:55 ` Vincent MAILHOL
2020-10-21 17:52 ` Oliver Hartkopp
2020-10-22 3:30 ` Vincent MAILHOL
2020-10-22 7:15 ` Oliver Hartkopp
2020-10-22 12:23 ` Vincent MAILHOL
2020-10-22 13:28 ` Oliver Hartkopp
2020-10-22 15:46 ` Vincent MAILHOL
2020-10-22 17:06 ` Oliver Hartkopp
2020-10-23 10:36 ` Vincent MAILHOL
2020-10-23 16:47 ` Oliver Hartkopp
2020-10-24 5:25 ` Vincent MAILHOL
2020-10-24 11:31 ` Oliver Hartkopp
2020-10-19 19:05 ` [net-rfc 05/16] can: dev: __can_get_echo_skb(): fix the returned length of CAN frame Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 06/16] can: can_create_echo_skb(): fix echo skb generation: always use skb_clone() Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 07/16] can: j1939: j1939_sk_bind(): return failure if netdev is down Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 08/16] can: isotp: Explain PDU in CAN_ISOTP help text Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 09/16] can: isotp: enable RX timeout handling in listen-only mode Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 10/16] can: ti_hecc: add missed clk_disable_unprepare() in error path Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 11/16] can: xilinx_can: handle failure cases of pm_runtime_get_sync Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 12/16] can: peak_usb: fix timestamp wrapping Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 13/16] can: peak_canfd: fix echo management when loopback is on Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 14/16] can: mcp251xfd: mcp251xfd_regmap_crc_read(): increase severity of CRC read error messages Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 15/16] can: mcp251xfd: mcp251xfd_regmap_nocrc_read(): fix semicolon.cocci warnings Marc Kleine-Budde
2020-10-19 19:05 ` [net-rfc 16/16] can: mcp251xfd: remove unneeded break Marc Kleine-Budde
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