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Subject: Re: [PATCH v6 2/5] mt76: mt76x02: split beaconing
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     nbd@nbd.name, linux-wireless@vger.kernel.org,
        lorenzo.bianconi@redhat.com
References: <20191119154746.20821-1-markus.theil@tu-ilmenau.de>
 <20191119154746.20821-3-markus.theil@tu-ilmenau.de>
 <20191120092803.GA517@redhat.com>
 <91b706b5-68b4-9679-a209-872f326de937@tu-ilmenau.de>
 <20191121125842.GB13833@redhat.com>
From:   Markus Theil <markus.theil@tu-ilmenau.de>
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Organization: TU Ilmenau
Message-ID: <2ddc33ca-b840-fe87-5881-0672076025cf@tu-ilmenau.de>
Date:   Thu, 21 Nov 2019 16:11:28 +0100
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On 21.11.19 13:58, Stanislaw Gruszka wrote:
> On Wed, Nov 20, 2019 at 11:27:55PM +0100, Markus Theil wrote:
>>>> -	}
>>>> -
>>>> -	for (i = bcn_idx; i < ARRAY_SIZE(dev->beacons); i++) {
>>>> -		if (!(dev->beacon_data_mask & BIT(i)))
>>>> -			break;
>>>> -
>>>> -		__mt76x02_mac_set_beacon(dev, i, NULL);
>>>> -	}
>>>>  
>>>>  	mt76_rmw_field(dev, MT_MAC_BSSID_DW1, MT_MAC_BSSID_DW1_MBEACON_N,
>>>>  		       bcn_idx - 1);
>>>> +
>>>> +	mt76_wr(dev, MT_BCN_BYPASS_MASK, 0xff00 | ~dev->beacon_data_mask);
>>> I'm not sure if this is correct for multi bss.
>>>
>>> In MT7620 manual BCM_BAYPASS_MASK is described as below:
>>>
>>> "
>>> Directly bypasses the Tx Beacon frame with the  specified 
>>> Beacon number. Bit0=Nth Beacon, bit1=(N- 1)th Beacon,... etc.
>>> N is the number of  Beacons defined in the  MULTI_BCN_NUM field in the 
>>> MAC_BSSID_DW1(offset: 0x1014) register.
>>> 0: Disable
>>> 1: Enable
>>> "
>>>
>>> Assuming manual is correct (it could be wrong) bypass mask should be
>>> calculated differently.
>>>
>>> Stanislaw
>>>
>> I tested the updated code with my usb nic and an mbss with 2 ap vifs.
>> Both beacons were transmitted. Maybe the manual is wrong in this place.
> If MAC_BSSID_DW1_MBEACON_N is set to 1 (2 beacons) according to manual
> bit0 is for second beacon slot and bit1 is for first beacon slot.
> Those bits are both marked at once, so no problem will happen.
>
> Problem may happen when you remove first vif/beacon. Then you will
> have bit1 marked in ->beacon_data_mask . But bit0 will be expect
> in BCM_BAYPASS_MASK by hardware (when MAC_BSSID_DW1_MBEACON_N=0)
>
> This scenarios can be extended to more vifs. So if you no longer 
> use bcn_idx and use vif_idx directly to point beacon slot/address.
> (ie. before for vif_idx 0,4,6, bcn_idx were 0,1,2 now there
> will be 0,4,6). You need to specify 7 (8 beacons) in
> MT_MAC_BSSID_DW1_MBEACON_N, and set bypass mask accordingly.
> For example:
>
> 	mt76_rmw_field(dev, MT_MAC_BSSID_DW1, MT_MAC_BSSID_DW1_MBEACON_N, 7);
> 	mask = 0;
> 	for (i = 0; i < 8; i++)
> 		if (dev->beacons[i])
> 			mask |= BIT(7 - i);
>
> 	mt76_wr(dev, MT_BCN_BYPASS_MASK, 0xff00 | ~mask);
>
> But again, this have to be tested. Ideally on mmio hardware which
> support more bssid's or on usb hardware with temporally increased
> num of bss limitation.
>
> Stanislaw
>
I'm currently fixing this. My next version will include the following for this aspect:
- clear beacon_data_mask before each round of setting beacons
- use ffz(dev->beacon_data_mask) to find next position and put next beacon in the corresponding slot
- as usb and mmio always copy the beacon, free_skb directly afterwards and drop the beacons array (the current code could leak memory for beacons in this array)

- permanently set the number of additional beacons to 7: mt76_rmw_field(dev, MT_MAC_BSSID_DW1, MT_MAC_BSSID_DW1_MBEACON_N, 7)
- updating the beacon bypass mask then becomes: mt76_wr(dev, MT_BCN_BYPASS_MASK, 0xff00 | ~bitrev8(dev->beacon_data_mask))

When I've tested this, I'll send an updated version.

Markus