On 07/31/2018 08:23 AM, Pankaj Bansal wrote: >> -----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) BTW: please update the "FLEXCAN hardware feature flags" table in the driver, add a CAN-FD column, too. >>>>> 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. I don't think this will make a big impact in reception speed, but relaxes the timing constraints instead. > 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) > Address offset (hex) (16 byte payload) > Address offset (hex) (32 byte payload) > Address offset (hex) (64 byte payload) This does look quite complex and could result in ugly code. First thing is to have a function that converts from mailbox number to mailbox address. 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 |
Attachment:
signature.asc
Description: OpenPGP digital signature
