Baochen Qiang <quic_bqiang@xxxxxxxxxxx> writes: > On 7/22/2024 2:54 PM, Baochen Qiang wrote: >> >> >> On 7/19/2024 10:10 PM, Jeff Johnson wrote: >>> On 7/14/2024 7:38 PM, Baochen Qiang wrote: >>>> 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. >>> >>> I asked for expert opinion on this patch and received the following response. >>> Baochen, can you take a look at this suggestion? >>> >>>> Aligning headers is sometimes done, but it appears the driver >>>> doesn't support scatter gather? I think the author may want to advertise >> right, ath12k does not support SG currently. >> >>>> scatter and linearize manually in the driver, to a correct offset. >> is there an existing skb API or API combinations which can do that >> for me? I checked __skb_linearize() and it does not take an 'offset' >> argument. > > or do I need to implement it myself from a very low level basis? like > (if required) allocating skb structure, allocating/aligning payload > buffer, copying/freeing paged frag/frag list, etc.. I don't know __skb_linearize() well enough to really comment here. I'm leaning towards we just take this patch to ath-current for v6.11 and, if needed, optimise it later. Thoughts? -- https://patchwork.kernel.org/project/linux-wireless/list/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
