> -----Original Message----- > From: Marc Kleine-Budde [mailto:mkl@xxxxxxxxxxxxxx] > Sent: Monday, July 30, 2018 8:51 PM > To: Pankaj Bansal <pankaj.bansal@xxxxxxx>; linux-can@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 4/6] net: can: flexcan: Add provision for variable > payload size > > On 07/30/2018 05:03 PM, Pankaj Bansal wrote: > >>> Till now the flexcan module supported 8 byte payload size as per CAN > >>> 2.0 specifications. > >>> But now upcoming flexcan module in NXP LX2160A SOC supports CAN > FD > >>> protocol too.The Message buffers need to be configured to have > >>> payload size greater than 8 bytes (if flexcan module supports it) > >>> > >>> Therefore, added provision in the driver for payload size to be variable. > >>> BUT, limit the only possible payload value to be 8, because the CAN > >>> FD changes are not in place yet. > >> > >> What's the size of a CAN-FD mailbox? Is it fixed or configurable at > runtime? > > > > Flexible mailboxes configurable to store 0 to 8, 16, 32 or 64 bytes > > data length > > Does it make any sense to store less than 64 bytes of data? What's the total > size of the mailbox then? IMO this makes sense in one scenario: if all the nodes in can network transmit data with < 64 bytes payload (say 32 bytes), then it would be beneficial to limit the payload size to 32 bytes, as this would increase number of RX buffers, which would help in reception speed. The total size of mailbox is Payload + 8 bytes (4 bytes for CAN ID and 4 bytes for CAN control bits; same as CAN 2.0 MB) The mailbox are allocated in memory as below: Address offset (hex) (8 byte payload) 0080 MB0 0090 MB1 00A0 MB2 00B0 MB3 00C0 MB4 00D0 MB5 .... .... Address offset (hex) (16 byte payload) 0080 MB0 0098 MB1 00B0 MB2 00C8 MB3 00E0 MB4 00F8 MB5 .... .... Address offset (hex) (32 byte payload) 0080 MB0 00A8 MB1 00D0 MB2 00F8 MB3 0120 MB4 0148 MB5 .... .... Address offset (hex) (64 byte payload) 0080 MB0 00C8 MB1 0110 MB2 0158 MB3 01A0 MB4 01E8 MB5 .... .... > > Marc > > -- > Pengutronix e.K. | Marc Kleine-Budde | > Industrial Linux Solutions | Phone: +49-231-2826-924 | > Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | > Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de | ��.n��������+%������w��{.n�����{����* jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
