On 30.08.2024 17:31:13, Martin Jocic wrote:
> Kvaser's PCIe cards uses the KCAN FPGA IP block which has dual 4K buffers for
> incoming messages shared by all (currently up to eight) channels. While the
> driver processes messages in one buffer, new incoming messages are stored in
> the other and so on.
>
> The design of KCAN is such that a buffer must be fully read and then released.
> Releasing a buffer will make the FPGA switch buffers. If the other buffer
> contains at least one incoming message the FPGA will also instantly issue a
> new interrupt, if not the interrupt will be issued after receiving the first
> new message.
>
> With IRQx interrupts, it takes a little time for the interrupt to happen,
> enough for any previous ISR call to do it's business and return, but MSI
> interrupts are way faster so this time is reduced to almost nothing.
>
> So with MSI, releasing the buffer HAS to be the very last action of the ISR
> before returning, otherwise the new interrupt might be "masked" by the kernel
> because the previous ISR call hasn't returned. And the interrupts are edge-
> triggered so we cannot loose one, or the ping-pong reading process will stop.
>
> This is why this patch modifies the driver to use a single write to the SRB_CMD
> register before returning.
>
> Signed-off-by: Martin Jocic <martin.jocic@xxxxxxxxxx>
Thanks for the detailed commit message. I've added a fixed tag:
Fixes: 26ad340e582d ("can: kvaser_pciefd: Add driver for Kvaser PCIEcan devices")
Thanks,
Marc
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