linux-kernel - Re: [PATCH] ath9k: fix build error with LEDS

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Date:   Mon, 25 Jan 2021 16:22:18 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     QCA ath9k Development <ath9k-devel@....qualcomm.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johannes Berg <johannes@...solutions.net>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Flavio Suligoi <f.suligoi@...m.it>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ath9k: fix build error with LEDS_CLASS=m

On Mon, Jan 25, 2021 at 4:04 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
> On Mon, 25 Jan 2021 at 15:38, Arnd Bergmann <arnd@...nel.org> wrote:
> > On Mon, Jan 25, 2021 at 2:27 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> I meant that having MAC80211_LEDS selected causes the ath9k driver to
> toggle on/off the WiFi LED. Every second, regardless whether it's
> doing something or not. In my setup, I have problems with a WiFi
> dongle somehow crashing (WiFi disappears, nothing comes from the
> dongle... maybe it's Atheros FW, maybe some HW problem) and I found
> this LED on/off slightly increases the chances of this dongle-crash.
> That was the actual reason behind my commits.
>
> Second reason is that I don't want to send USB commands every second
> when the device is idle. It unnecessarily consumes power on my
> low-power device.

Ok, I see.

> Of course another solution is to just disable the trigger via sysfs
> LED API. It would also work but my patch allows entire code to be
> compiled-out (which was conditional in ath9k already).
>
> Therefore the patch I sent allows the ath9k LED option to be fully
> choosable. Someone wants every-second-LED-blink, sure, enable
> ATH9K_LEDS and you have it. Someone wants to reduce the kernel size,
> don't enable ATH9K_LEDS.

Originally, I think this is what CONFIG_MAC80211_LEDS was meant
for, but it seems that this is not actually practical, since this also
gets selected by half of the drivers using it, while the other half have
a dependency on it. Out of the ones that select it, some in turn
select LEDS_CLASS, while some depend on it.

I think this needs a larger-scale cleanup for consistency between
(at least) all the wireless drivers using LEDs. Either your patch
or mine should get applied in the meantime, and I don't care much
which one in this case, as we still have the remaining inconsistency.

        Arnd