Received-SPF: pass (google.com: best guess record for domain of linux-wireless-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190503072146.49999-1-chiu@endlessm.com> <20190503072146.49999-3-chiu@endlessm.com>
 <CAD8Lp47_-6d2wCAs5QbuR6Mw2w91TyJ9W3kFiJHH4F_6dXqnHg@mail.gmail.com>
 <CAB4CAweQXz=wQGA5t7BwWYdwbRrHCji+BWc0G52SUcZFGc8Pnw@mail.gmail.com>
 <CAD8Lp46hcx0ZHFMUdXdR6unbeMQJsfyuEQ7hUFpHY2jU9R7Gcw@mail.gmail.com> <CAB4CAwf26pdCY7FJA5H7d1aEY2xpjSto4JxARwczmVJ==41yng@mail.gmail.com>
In-Reply-To: <CAB4CAwf26pdCY7FJA5H7d1aEY2xpjSto4JxARwczmVJ==41yng@mail.gmail.com>
From:   Daniel Drake <drake@endlessm.com>
Date:   Tue, 21 May 2019 12:38:22 -0600
Message-ID: <CAD8Lp47K0Jn2wotANdQV3kT9yPP7bLnVd0eYhWui-vNDOEXBTA@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>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

On Fri, May 10, 2019 at 2:37 AM Chris Chiu <chiu@endlessm.com> wrote:
> I've verified that multiple virtual interface can not work simultaneously in
> STA mode. I assigned different mac address for different vifs, I can only
> bring only one interface up. If I want to bring the second vif up, it always
> complains "SIOCSIFFLAGS: Device or resource busy".

Interesting. Can you go deeper into that so that we can be more
confident of this limitation?

ieee80211_open() is the starting point.
ieee80211_check_concurrent_iface() is one candidate to generate -EBUSY
but from inspection, I don't think that's happening in this case,
perhaps you can keep following through in order to figure out which
part of the code is not allowing the 2nd STA interface to come up.

Daniel