[report] wifi: mt76: mt7996: fix FCS error flag check in RX descriptor

[Ben Greear]

Hello Peter,

To help understand the severity of this problem, can you let us know when
the incorrect bit is set?  In other words, would looking at the wrong bit
erroneously cause good frames to be dropped, or was the bit always zero and
it just allowed bad frames to be accepted?

Thanks,
Ben

On 10/12/25 20:19, Peter Chiu wrote:
> On Sun, 2025-10-12 at 22:02 +0530, ALOK TIWARI wrote:
> 
> Hi Alok,
> 
> Thanks for your mail.
> Your understanding is correct.
> There is a typo in mt7996.
> 
> Thanks,
> Peter Chiu
> 
>> 
>> External email : Please do not click links or open attachments until
>> you have verified the sender or the content.
>> 
>> 
>> Hi,
>> 
>> While looking through the FCS error handling in the mt76 drivers,
>> I noticed that mt7996 uses rxd1 to check the MT_RXD3_NORMAL_FCS_ERR
>> bit,
>> whereas other Connac3-based drivers (such as mt7925) use rxd3.
>> 
>> According to the definitions, MT_RXD3_NORMAL_FCS_ERR is located in
>> the
>> fourth
>> RX descriptor word (rxd3), so I prepared a small patch to switch the
>> check from
>> rxd1 to rxd3 for consistency and correctness.
>> 
>> Before sending it formally, I wanted to confirm whether this
>> understanding is correct.
>> is mt7996 indeed supposed to use rxd3 for this flag, like mt7925?
>> 
>> Fixes: 98686cd21624 ("wifi: mt76: mt7996: add driver for MediaTek Wi-
>> Fi
>> 7 (802.11be) devices")
>> 
>> Thanks,
>> Alok
>> 
>> ---
>>   drivers/net/wireless/mediatek/mt76/mt7996/mac.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
>> b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
>> index 9501def3e0e3..59744e5593b6 100644
>> --- a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
>> +++ b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
>> @@ -527,7 +527,7 @@ mt7996_mac_fill_rx(struct mt7996_dev *dev, enum
>> mt76_rxq_id q,
>>              !(csum_status & (BIT(0) | BIT(2) | BIT(3))))
>>                  skb->ip_summed = CHECKSUM_UNNECESSARY;
>> 
>> -       if (rxd1 & MT_RXD3_NORMAL_FCS_ERR)
>> +       if (rxd3 & MT_RXD3_NORMAL_FCS_ERR)
>>                  status->flag |= RX_FLAG_FAILED_FCS_CRC;
>> 
>>          if (rxd1 & MT_RXD1_NORMAL_TKIP_MIC_ERR)
>> --
>> 2.50.1
> 
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-- 
Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com