Re: [PATCH v2 2/2] mwifiex: Try waking the firmware until we get an interrupt

Hi,

On Sun, Oct 3, 2021 at 2:18 AM Jonas Dreßler verdre@v0yd.nl wrote:

So I think I have another solution that might be a lot more elegant, how about this:

try_again: n_tries++;

    mwifiex_write_reg(adapter, reg->fw_status, FIRMWARE_READY_PCIE);

    if (wait_event_interruptible_timeout(adapter->card_wakeup_wait_q,
                                         READ_ONCE(adapter->int_status) != 0,
                                         WAKEUP_TRY_AGAIN_TIMEOUT) == 0 &&
        n_tries < MAX_N_WAKEUP_TRIES) {
            goto try_again;
    }

Isn't wait_event_interruptible_timeout()'s timeout in jiffies, which is not necessarily that predictable, and also a lot more coarse-grained than we want? (As in, if HZ=100, we're looking at precision on the order of 10ms, whereas the expected wakeup latency is ~6ms.) That would be OK for well-behaved PCI cases, where we never miss a write, but it could ~double your latency for your bad systems that will need more than one run of the loop.

Also, feels like a do/while could be cleaner, but that's a lesser detail.

and then call wake_up_interruptible() in the mwifiex_interrupt_status() interrupt handler.

This solution should make sure we always keep wakeup latency to a minimum and can still retry the register write if things didn't work.

Brian