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From:   Daniel Drake <drake@endlessm.com>
Date:   Mon, 27 May 2019 10:40:49 -0600
Message-ID: <CAD8Lp45OtJG2V1F9Ybwav7RUs572Q88d2VF4YX1xjy=n5wsvEA@mail.gmail.com>
Subject: Re: [RFC PATCH 2/2] rtl8xxxu: Add watchdog to update rate mask by
 signal strength
To:     Chris Chiu <chiu@endlessm.com>
Cc:     Jes Sorensen <jes.sorensen@gmail.com>,
        Kalle Valo <kvalo@codeaurora.org>,
        David Miller <davem@davemloft.net>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Linux Upstreaming Team <linux@endlessm.com>,
        Larry Finger <Larry.Finger@lwfinger.net>
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On Mon, May 27, 2019 at 12:38 AM Chris Chiu <chiu@endlessm.com> wrote:
> The -EBUSY is returned by the ieee80211_check_combinations() in the
> ieee80211_check_concurrent_iface() function which is invoked each time
> doing ieee80211_open().
> The ieee80211_check_combinations() returns the -EBUSY because of
> cfg80211_check_combinations() will iterate all interfaces of different types
> then checks the combination is valid or not, which in this case the number
> of interface combination accumulated by cfg80211_iter_sum_ifcombos is 0
> when I'm trying to bring up the second station interface.

Thanks for clarifying. I see, rtl8xxxu does not provide any
iface_combinations so the default is to reject parallel interfaces.

Given that we can now confidently say that multiple interfaces are not
supported, I think that inside rtl8xxxu_add_interface() you could
store a pointer to the vif inside the rtl8xxxu_priv structure (and
clear it in rtl8xxxu_remove_interface). Plus for clarity, add a
comment pointing out that only a single interface is supported, and
make rtl8xxxu_add_interface() acually fail if we already had a
non-NULL pointer stored in the priv structure.

Then you can simplify the patch to remove the ugly storing of vif
inside rtl8xxxu_watchdog. You can store the delayed_work in the main
priv struct too, dropping rtl8xxxu_watchdog altogether.

Daniel