Question on beacon-miss offloading.

Ben Greear greearb at
Mon Jun 15 08:35:12 PDT 2015

On 06/14/2015 10:36 PM, Michal Kazior wrote:
> On 12 June 2015 at 17:37, Ben Greear <greearb at> wrote:
>> On 06/11/2015 11:03 PM, Michal Kazior wrote:
>>> On 12 June 2015 at 01:38, Ben Greear <greearb at> wrote:
>>>> On 06/11/2015 02:07 PM, Ben Greear wrote:
>>>>> In my ath10k CT firmware, I am disabling the beacon-miss offloading
>>>>> to save space and because it will not work with lots of virtual
>>>>> stations.
>>>>> But, it must be that I need some way to tell the stack that this
>>>>> feature is not enabled, because when suddenly kill my AP, then
>>>>> the ath10k station connected to it shows endless 'beacon loss' events
>>>>> in 'iw events' output, but it never actually loses connection.
>>>>> Stock firmware works fine, so probably I just need to disable
>>>>> some feature flag when registering the ath10k hardware
>>>>> when using CT firmware.
>>>>> With stock firmware, I see a quick dissassociation due to inactivity.
>>>>> I am having poor luck finding how a driver tells the stack
>>>>> it has beacon miss offload or not, so, does anyone know how
>>>>> this is controlled?
>>>> I still am not sure why stock firmware works, but it appears
>>>> the reason mine is failing is that the ACK status for mgt frames
>>>> is always set to TRUE since the ath10k wmi-mgt-tx API is so
>>>> lame.  So, mac80211 does a probe, ath10k lies and says it was
>>>> acked, and mac80211 then things all is well for another few
>>>> seconds.
>>> mac80211 shouldn't do a Probe Req to an AP on beacon loss because
>>> ath10k advertises it supports tx-status report. Hence mac80211 should
>>> use NullFunc frames which shouldn't go through wmi-mgmt-tx but htt
>>> tx-frm.
>>> But then again: NullFunc status reporting via htt tx-frm was broken on
>>> 10.1 if memory serves right. I believe it was fixed in 10.2 or 10.2.4.
>>> This problem has been effectively obscured on stock 10.1 by the
>>> offloaded beacon miss.
>> Thanks for the hint.  I was able to fix my firmware to properly
>> return htt tx status, and now it appears to work properly.
>> A quick throughput test works as well, so hopefully no regressions.
>> I guess the NulFunc related comment is incorrect for 10.1 stock firmware?
>> Maybe some others?
>> static void ath10k_tx_htt(struct ath10k *ar, struct sk_buff *skb)
>> {
>>         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
>>         int ret = 0;
>>         if (ar->htt.target_version_major >= 3) {
>>                 /* Since HTT 3.0 there is no separate mgmt tx command */
>>                 ret = ath10k_htt_tx(&ar->htt, skb);
>>                 goto exit;
>>         }
>>         if (ieee80211_is_mgmt(hdr->frame_control)) {
>>                 if (test_bit(ATH10K_FW_FEATURE_HAS_WMI_MGMT_TX,
>>                              ar->fw_features)) {
>>                         if (skb_queue_len(&ar->wmi_mgmt_tx_queue) >=
>>                             ATH10K_MAX_NUM_MGMT_PENDING) {
>>                                 ath10k_warn(ar, "reached WMI management transmit queue limit\n");
>>                                 ret = -EBUSY;
>>                                 goto exit;
>>                         }
>>                         skb_queue_tail(&ar->wmi_mgmt_tx_queue, skb);
>>                         ieee80211_queue_work(ar->hw, &ar->wmi_mgmt_tx_work);
>>                 } else {
>>                         ret = ath10k_htt_mgmt_tx(&ar->htt, skb);
>>                 }
>>         } else if (!test_bit(ATH10K_FW_FEATURE_HAS_WMI_MGMT_TX,
>>                              ar->fw_features) &&
>>                    ieee80211_is_nullfunc(hdr->frame_control)) {
>>                 /* FW does not report tx status properly for NullFunc frames
>>                  * unless they are sent through mgmt tx path. mac80211 sends
>>                  * those frames when it detects link/beacon loss and depends
>>                  * on the tx status to be correct. */
>>                 ret = ath10k_htt_mgmt_tx(&ar->htt, skb);
>>         } else {
>>                 ret = ath10k_htt_tx(&ar->htt, skb);
>>         }
> The NullFunc workaround was originally done for 999.999.0.636 but
> should be true for 10.1 as well with the sole exception the latter
> doesn't have htt-mgmt-tx to workaround the problem.

Is it correct to say that this logic is completely broken for stock 10.1 firmware
because null-func frames are not management frames, so the packet goes out the
ath10k_htt_mgmt_tx call, and stock 10.1 does not properly do tx status
for htt-tx frames?

And slightly different question:  Once I put in proper htt ACK reporting into
my firmware, I notice that stations often loose connectivity when they are
idle.  I captured a sniff, and it appears the null-func packets are sent,
but the header is not requesting an explicit ACK, and the AP does not ACK it,
so connection is lost.

I guess that the null-func frames should be requesting explicit ACK?


Ben Greear <greearb at>
Candela Technologies Inc

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