In transmit path, it is likely that the iova is not aligned to PCIe TLP
max payload size, which is 128 for WCN7850. Normally in such cases hardware
is expected to split the packet into several parts in a manner such that
they, other than the first one, have aligned iova. However due to hardware
limitations, WCN7850 does not behave like that properly with some specific
unaligned iova in transmit path. This easily results in target hang in a
KPI transmit test: packet send/receive failure, WMI command send timeout
etc. Also fatal error seen in PCIe level:
...
Capabilities: ...
...
DevSta: ... FatalErr+ ...
...
...
Work around this by manually moving/reallocating payload buffer such that
we can map it to a 128 bytes aligned iova. The moving requires sufficient
head room or tail room in skb: for the former we can do ourselves a favor
by asking some extra bytes when registering with mac80211, while for the
latter we can do nothing.
Moving/reallocating buffer consumes additional CPU cycles, but the good news
is that an aligned iova increases PCIe efficiency. In my tests on some X86
platforms the KPI results are almost consistent.
Since this is seen only with WCN7850, add a new hardware parameter to
differentiate from others.
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Cc: <stable@vger.kernel.org>
Tested-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://patch.msgid.link/20240715023814.20242-1-quic_bqiang@quicinc.com
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