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From: Kalle Valo <kvalo@kernel.org>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>,
  ath12k@lists.infradead.org,  linux-wireless@vger.kernel.org
Subject: Re: [PATCH v2 3/3] wifi: ath12k: Add lock to protect the hardware
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	<517caf852d37b3803bcf087a6b575f2ecdb5ba10.camel@sipsolutions.net>
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	<0bfbb5549b48296e6219488d47caccd10e818700.camel@sipsolutions.net>
Date: Wed, 24 Apr 2024 15:16:50 +0300
In-Reply-To: <0bfbb5549b48296e6219488d47caccd10e818700.camel@sipsolutions.net>
	(Johannes Berg's message of "Wed, 24 Apr 2024 11:52:22 +0200")
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Johannes Berg <johannes@sipsolutions.net> writes:

> On Wed, 2024-04-24 at 12:50 +0300, Kalle Valo wrote:
>> Johannes Berg <johannes@sipsolutions.net> writes:
>> 
>> > On Wed, 2024-04-24 at 12:39 +0300, Kalle Valo wrote:
>> > > 
>> > > Exactly. Swithing to use wiphy_lock() definitely one of my longterm
>> > > goals in ath12k. I already started working on switching ath12k to use
>> > > wiphy_lock() but IIRC I got blocked by not being able to call
>> > > wiphy_delayed_work_cancel() without taking wiphy_lock.
>> > 
>> > That's because I didn't want to have an async version, but theoretically
>> > we could have a version of it that just cancels the timer. If you don't
>> > hold the wiphy mutex already you could even wait for it to finish. It
>> > just adds more complexity there, and I was trying to make it all a lot
>> > more obvious :)
>> 
>> Yeah, understandable. I think changing ath12k WMI event handling to use
>> wiphy_work makes sense, running them in tasklet context feels overkill.
>
> Maybe. Note that the wiphy lock _can_ create delays etc. here, if you're
> doing other configuration work at the same time, or similar. Though I
> guess eventually you need locking there anyway, to access the HW. So it
> can be a bit of a trade-off.
>
> I expect this will evolve over time even in mac80211, though so far we
> haven't seen any bad effect from it.

Good point. And now that I think of this more I don't think we can use
wiphy_work with WMI events as we are waiting some events while holding
wiphy_lock, that would end up as deadlock. So most likely we need to use
a normal workqueue with WMI events and take wiphy_lock manually in
certain cases. But I'll need to investigate more and do some
experiments.

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