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

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Date:   Tue, 01 Sep 2020 15:14:31 +0300
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Brian Norris <briannorris@...omium.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        ath10k <ath10k@...ts.infradead.org>,
        Rakesh Pillai <pillair@...eaurora.org>,
        netdev <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Abhishek Kumar <kuabhs@...gle.com>
Subject: Re: [PATCH v2 1/2] ath10k: Keep track of which interrupts fired, don't poll them

Doug Anderson <dianders@...omium.org> writes:

> 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?

I have the hardware but in practise no time to do the testing :/

> ...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?

Basically I would like to see some evidence in the commit log that _all_
hardware families are taken into account to avoid any regressions, be it
testing or at least thorough review. I see way too many patches where
people are working just on one hardware/firmware combo and not giving a
single thought how it would work on other hardware.

But I applied the three patches now, let's hope they are ok. At least I
was not able to find any problems during review, but of course real
testing would be better than just review.

-- 
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