Re: [PATCH v8] net: airoha: npu: use cacheline-sized buffers for mailbox DMA

Jakub Kicinski <[email protected]> Mon, 17 Aug 2026 16:17:56 -0700

Newsgroups	org.kernel.vger.netdev,org.infradead.lists.linux-arm-kernel,org.infradead.lists.linux-mediatek
Message-ID	<[email protected]>

On Mon, 17 Aug 2026 11:06:01 +0200 Daniel Pawlik wrote:
> On EN7581 + MT7996 (Gemtek W1700K), mapping small caller buffers with
> DMA_BIDIRECTIONAL regresses NPU version probe: the mailbox completes
> successfully but WLAN_FUNC_GET_WAIT_NPU_VERSION reads as 0.0 instead of
> 0.1111.
> 
> Allocate at least SMP_CACHE_BYTES for each mailbox payload and map
> ALIGN(len, SMP_CACHE_BYTES) with DMA_BIDIRECTIONAL while programming
> the original payload length into the mailbox length register.
> 
> Tested on Quantum Fiber / Gemtek W1700K (EN7581 + MT7996), kernel
> 6.18.44, including two cold reboots and sustained WiFi use.

To me the fact that this patch helps only proves that the swiotlb
implementation on this platform is wonky, no?
IOW AFAIU we are avoiding the bounce buffer so things work, but
the bounce buffer is still broken?