Re: [PATCH 1/2] mwifiex: Use non-posted PCI register writes

On Sat, Sep 18, 2021 at 12:37 AM Jonas Dreßler [off-list ref] wrote:

Thanks for the pointer to that commit Brian, it turns out this is
actually the change that causes the "Firmware wakeup failed" issues that
I'm trying to fix with the second patch here.

Huh. That's interesting, although I guess it makes some sense given
your theory of "dropped writes". FWIW, this strategy (post a single
write, then wait for wakeup) is the same used by some other
chips/drivers too (e.g., ath10k/pci), although in those cases card
wakeup is much much faster. But if the bus was dropping writes
somehow, those strategies would fail too.

Also my approach is a lot messier than just reverting
062e008a6e83e7c4da7df0a9c6aefdbc849e2bb3 and also appears to be blocking
even longer...

For the record, in case you're talking about my data ("blocking even
longer"): I was only testing patch 1. Patch 2 isn't really relevant to
my particular systems (Rockchip RK3399 + Marvell 8997/PCIe), because
(a) I'm pretty sure my system isn't "dropping" any reads or writes
(b) all my delay is in the read-back; the Rockchip PCIe bus is waiting
indefinitely for the card to wake up, instead of timing out and
reporting all-1's like many x86 systems appear to do (I've tested
this).

So, the 6ms delay is entirely sitting in the ioread32(), not a delay loop.

I haven't yet tried your version 2 (which avoids the blocking read to
wake up; good!), but it sounds like in theory it could solve your
problem while avoiding 6ms delays for me. I intend to test your v2
this week.

Does anyone have an idea what could be the reason for the posted write
not going through, or could that also be a potential firmware bug in the
chip?

I have no clue about that. That does sound downright horrible, but so
are many things when dealing with this family of hardware/firmware.
I'm not sure how to prove out whether this is a host bus problem, or
an endpoint/firmware problem, other than perhaps trying the same
module/firmware on another system, if that's possible.

Anyway, to reiterate: I'm not fundamentally opposed to v2 (pending a
test run here), even if it is a bit ugly and perhaps not 100%
understood.

Brian