netdev - Re: [PATCH v2 1/2] ath10k: Keep track of which interrupts fired, don't poll them

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Date:   Wed, 26 Aug 2020 07:59:52 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Kalle Valo <kvalo@...eaurora.org>
Cc:     ath10k <ath10k@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Brian Norris <briannorris@...omium.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Rakesh Pillai <pillair@...eaurora.org>,
        Abhishek Kumar <kuabhs@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] ath10k: Keep track of which interrupts fired,
 don't poll them

Hi,

On Wed, Aug 26, 2020 at 7:51 AM Kalle Valo <kvalo@...eaurora.org> wrote:
>
> Douglas Anderson <dianders@...omium.org> 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@...omium.org>
> > Reviewed-by: Rakesh Pillai <pillair@...eaurora.org>
> > Reviewed-by: Brian Norris <briannorris@...omium.org>
> > Signed-off-by: Kalle Valo <kvalo@...eaurora.org>
>
> My main concern of this patch is that there's no info how it works on other
> hardware families. For example, QCA9984 is very different from WCN3990. The
> best would be if someone can provide a Tested-on tags for other hardware (even
> some of them).

I simply don't have access to any other Atheros hardware.  Hopefully
others on this thread do, though?  ...but, if nothing else, I believe
code inspection shows that the only places that are affected by the
changes here are:

* Wifi devices that use "snoc.c".  The only compatible string listed
in "snoc.c" is wcn3990.

* Wifi devices that set "per_ce_irq" to true.  The only place in the
table where this is set to true is wcn3990.

While it is certainly possible that I messed up and somehow affected
other WiFi devices, the common bits of code in "ce.c" and "ce.h" are
fairly easy to validate so hopefully they look OK?

-Doug