rtlwifi/rtl8192cu AP mode broken with PS STA

From: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
To: Ping-Ke Shih <pkshih@realtek.com>, Kalle Valo <kvalo@codeaurora.org>
Cc: Johannes Berg <johannes@sipsolutions.net>,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: rtlwifi/rtl8192cu AP mode broken with PS STA
Date: Mon, 29 Mar 2021 00:54:28 +0200	[thread overview]
Message-ID: <e2924d81-0e30-2dd0-292b-428fea199484@maciej.szmigiero.name> (raw)

Hi,

It looks like rtlwifi/rtl8192cu AP mode is broken when a STA is using PS,
since the driver does not update its beacon to account for TIM changes,
so a station that is sleeping will never learn that it has packets
buffered at the AP.

Looking at the code, the rtl8192cu driver implements neither the set_tim()
callback, nor does it explicitly update beacon data periodically, so it
has no way to learn that it had changed.

This results in the AP mode being virtually unusable with STAs that do
PS and don't allow for it to be disabled (IoT devices, mobile phones,
etc.).

I think the easiest fix here would be to implement set_tim() for example
the way rt2x00 driver does: queue a work or schedule a tasklet to update
the beacon data on the device.

Thanks,
Maciej