Subhasish Ghosh wrote:
> The CAN controller that I am using allows configuring per-mailbox IDs.
> CAN being a broadcast network, this feature reduces the interrupts to
> the processor.
>
> From Documentation/can.txt, what I understand is that the socketcan
> interface does not provide any mechanism to configure the h/w for this
> purpose (chapter 6.3).
>
> Instead, the h/w is configured to receive all identifiers and the
> filtering is done on the stack (like ti_hecc.c) and to avoid hogging the
> processor some interrupt mitigation techniques like NAPI is implemented.
>
> Isn't this a work around?
No it's not.
Remember that you're working in a multi-user system now, and therefore it's
not defined what all of your user-apps need from the specific CAN bus.
For that reason the implementation of efficient filters is done in the
soft-IRQ that's called right after the (hard-) interrupt routine of the CAN
driver.
Having a generic CAN driver interface is one of the major motivations for
SocketCAN. You really don't want to have hardware-specific ("N mailboxes")
configuration interfaces which leads into a maintenance hell.
> My question is, did I miss something, is there any way to configure the
> h/w for this purpose. Is it a good idea if I cook up a sysfs interface
> for my driver for this.
The problem is, that a filtering on driver level affects *every* user in the
system.
So far no one discovered a problem with the irq-load of CAN drivers in his
system. We've been running a 133MHz PowerPC with four SJA1000 controllers for
years ...
If you really(!) get into problems, we should discuss a netlink configuration
option for driver-level CAN-ID filtering (also abstracted from "mailboxes").
But please check if it's really needed and if you probably have a different
view on the general approach of SocketCAN now.
Best regards,
Oliver
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