[BUG] ath12k: CSA with blocktx disrupts TX on other bands

[Remi Pommarel <repk@triplefau.lt>]

Hi,

With the single phy changes introduced for MLO support, both 2.4 GHz
and 5 GHz interfaces on the same dual-band chip now share the same
hardware queues, even when operating on separate bands.

As a result, when a Channel Switch Announcement (CSA) with blocktx
is triggered on one interface (e.g., the 5 GHz vif),
ieee80211_vif_block_queues_csa() pauses the shared HW queues. This
unintentionally blocks TX traffic on the other interface (e.g., the
2.4 GHz vif), despite it being on a different band.

I haven't tested it, but the same issue is expected to affect a single
MLO AP setup, where a CSA could inadvertently pause transmission across
all links.

To address this class of problem, the IEEE80211_HW_HANDLES_QUIET_CSA
flag was introduced. When set, it delegates queue pausing to the
firmware, avoiding unnecessary disruptions in multi-vif or MLO
scenarios. This approach is already used in iwlwifi/mvm, as seen in
commit bbd6d0f8bc51 ("wifi: iwlwifi: mvm: advertise
IEEE80211_HW_HANDLES_QUIET_CSA").

Thus, does the current ath12k firmware properly handle TX quiescing
allowing IEEE80211_HW_HANDLES_QUIET_CSA to be set ? Or does it need
to be handle at the driver level (likewise what has been done in
iwlwifi/mvm in the commit above) ?

Thanks.

-- 
Remi