Re: [PATCH] usb: typec: ucsi: Clear pending after acking connector change

Hi,

On Mon, May 17, 2021 at 01:03:12PM +0300, Heikki Krogerus wrote:

On Sat, May 15, 2021 at 09:09:53PM -0700, Bjorn Andersson wrote:

quoted

It's possible that the interrupt handler for the UCSI driver signals a
connector changes after the handler clears the PENDING bit, but before
it has sent the acknowledge request. The result is that the handler is
invoked yet again, to ack the same connector change.

At least some versions of the Qualcomm UCSI firmware will not handle the
second - "spurious" - acknowledgment gracefully. So make sure to not
clear the pending flag until the change is acknowledged.

Any connector changes coming in after the acknowledgment, that would
have the pending flag incorrectly cleared, would afaict be covered by
the subsequent connector status check.

Fixes: 217504a05532 ("usb: typec: ucsi: Work around PPM losing change information")
Signed-off-by: Bjorn Andersson <redacted>

I'm OK with this if Bejamin does not see any problems with it. I'll
wait for his comments before giving my reviewed-by tag.

That workaround (commit 217504a05532) is unfortunately too fragile.
I'm going to now separate the processing of the connector state from
the event handler (interrupt handler). That way we should be fairly
sure we don't loose any of the connector states even if an event is
generated while we are still in the middle of processing the previous
one(s), and at the same time be sure that we also don't confuse the
firmware.

So the event handler shall after that only read the connector status,
schedule the unique job where it's processed and ACK the event.
Nothing else.

Seems to be straightforward to implement. I'm attaching the patch I
made for that. I think it should actually also remove the problem you
are seeing. Can you test it?

thanks,

-- 
heikki