Kalle,

On Thu, Jul 9, 2020 at 8:22 AM Douglas Anderson [off-list ref] wrote:

If we have a per CE (Copy Engine) IRQ then we have no summary
register.  Right now the code generates a summary register by
iterating over all copy engines and seeing if they have an interrupt
pending.

This has a problem.  Specifically if _none_ if the Copy Engines have
an interrupt pending then they might go into low power mode and
reading from their address space will cause a full system crash.  This
was seen to happen when two interrupts went off at nearly the same
time.  Both were handled by a single call of ath10k_snoc_napi_poll()
but, because there were two interrupts handled and thus two calls to
napi_schedule() there was still a second call to
ath10k_snoc_napi_poll() which ran with no interrupts pending.

Instead of iterating over all the copy engines, let's just keep track
of the IRQs that fire.  Then we can effectively generate our own
summary without ever needing to read the Copy Engines.

Tested-on: WCN3990 SNOC WLAN.HL.3.2.2-00490-QCAHLSWMTPL-1

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Rakesh Pillai <redacted>
Reviewed-by: Brian Norris <briannorris@chromium.org>
---
This patch continues work to try to squash all instances of the crash
we've been seeing while reading CE registers and hopefully this patch
addresses the true root of the issue.

The first patch that attempted to address these problems landed as
commit 8f9ed93d09a9 ("ath10k: Wait until copy complete is actually
done before completing").  After that Rakesh Pillai posted ("ath10k:
Add interrupt summary based CE processing") [1] and this patch is
based atop that one.  Both of those patches significantly reduced the
instances of problems but didn't fully eliminate them.  Crossing my
fingers that they're all gone now.

[1] https://lore.kernel.org/r/1593193967-29897-1-git-send-email-pillair@codeaurora.org (local)

Changes in v2:
- Add bitmap_clear() in ath10k_snoc_hif_start().

 drivers/net/wireless/ath/ath10k/ce.c   | 84 ++++++++++----------------
 drivers/net/wireless/ath/ath10k/ce.h   | 14 ++---
 drivers/net/wireless/ath/ath10k/snoc.c | 19 ++++--
 drivers/net/wireless/ath/ath10k/snoc.h |  1 +
 4 files changed, 52 insertions(+), 66 deletions(-)

I'm wondering if there's anything else you're looking for here.  If I
just need to sit tight that's fine, but I want to make sure this patch
isn't lost and you're not waiting for any actions on my part.  The
patch it depends on from Rakesh (see above or patchwork ID 11628289)
is also still marked as "Under Review".

We have been using this patch for the last few months and we haven't
hit a single crash like we were getting before.  At the same time, we
haven't found any regressions that have been attributed to this patch.

Anyway, just figured I'd check in.  Thanks!

-Doug