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Thu, 20 Aug 2026 02:00:02 -0700 (PDT) Received: from fedora ([46.205.218.68]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499aa1111b2sm176837215e9.5.2026.08.20.02.00.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Aug 2026 02:00:01 -0700 (PDT) From: Daniel Pawlik To: netdev@vger.kernel.org Cc: linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org, kuba@kernel.org, lorenzo@kernel.org, nbd@nbd.name, sean.wang@mediatek.com, Mark-MC.Lee@mediatek.com, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, yangshiji66@outlook.com, Daniel Pawlik Subject: [PATCH v10 2/2] net: airoha: npu: use cacheline-sized buffers for mailbox DMA Date: Thu, 20 Aug 2026 10:59:41 +0200 Message-ID: <20260820085941.380401-2-pawlik.dan@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260820085941.380401-1-pawlik.dan@gmail.com> References: <20260820085941.380401-1-pawlik.dan@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260820_020004_646341_3AEBBD47 X-CRM114-Status: GOOD ( 15.96 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On non-coherent ARM64 (EN7581), the kernel's dma_direct_map_page() forces swiotlb bounce buffering when: !IS_ALIGNED(phys | size, dma_get_cache_alignment()) The NPU mailbox buffers are 12-24 bytes, well below the 64-byte cache line size, so this check always fails regardless of physical address alignment. The swiotlb sync path itself works correctly, but the EN7581 NPU cannot DMA-write to the swiotlb bounce buffer address range — it reads commands fine (mbox_status=0x7 success) but never writes responses back, leaving response fields as zeros. This was confirmed through five boot traces on a Gemtek W1700K: - Boots 1-4: all streaming DMA through swiotlb (is_swiotlb=1), bounce buffer byte-identical to pre-map after NPU completion, even after explicit CPU cache invalidation (dcache_inval_poc). NPU version reads 0.0. - Boot 5: kmalloc'd cache-line-aligned buffer bypasses swiotlb (is_swiotlb=0 on all 169 mappings), NPU writes response data directly, version reads 0.1111, WiFi fully functional. Fix by rounding mailbox buffer allocations up to dma_get_cache_alignment() and mapping the rounded length. The original payload size is still programmed into the mailbox length register. kmalloc returns cache-line-aligned pointers on ARM64 for allocations >= ARCH_KMALLOC_MINALIGN, so the IS_ALIGNED check passes and swiotlb is not triggered. Fixes: 6f884eb87a79 ("net: airoha: Fix DMA direction for NPU mailbox buffer") Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20260814110017.2795022-1-pawlik.dan@gmail.com/ Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20260809152813.585797-1-pawlik.dan@gmail.com/ Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20260805070851.2885888-1-pawlik.dan@gmail.com/ Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Daniel Pawlik --- drivers/net/ethernet/airoha/airoha_npu.c | 25 +++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/drivers/net/ethernet/airoha/airoha_npu.c b/drivers/net/ethernet/airoha/airoha_npu.c index 4045d1eb93ea..3416f921f961 100644 --- a/drivers/net/ethernet/airoha/airoha_npu.c +++ b/drivers/net/ethernet/airoha/airoha_npu.c @@ -5,6 +5,7 @@ */ #include +#include #include #include #include @@ -160,15 +161,21 @@ struct wlan_mbox_data { DECLARE_FLEX_ARRAY(u8, d); }; +static size_t airoha_npu_mbox_size(size_t len) +{ + return ALIGN(len, dma_get_cache_alignment()); +} + static int airoha_npu_send_msg(struct airoha_npu *npu, int func_id, void *p, int size) { u16 core = 0; /* FIXME */ u32 val, offset = core << 4; dma_addr_t dma_addr; + size_t map_len = airoha_npu_mbox_size(size); int ret; - dma_addr = dma_map_single(npu->dev, p, size, DMA_BIDIRECTIONAL); + dma_addr = dma_map_single(npu->dev, p, map_len, DMA_BIDIRECTIONAL); ret = dma_mapping_error(npu->dev, dma_addr); if (ret) return ret; @@ -191,7 +198,7 @@ static int airoha_npu_send_msg(struct airoha_npu *npu, int func_id, spin_unlock_bh(&npu->cores[core].lock); - dma_unmap_single(npu->dev, dma_addr, size, DMA_BIDIRECTIONAL); + dma_unmap_single(npu->dev, dma_addr, map_len, DMA_BIDIRECTIONAL); return ret; } @@ -333,7 +340,7 @@ static int airoha_npu_ppe_init(struct airoha_npu *npu) struct ppe_mbox_data *ppe_data; int err; - ppe_data = kzalloc_obj(*ppe_data); + ppe_data = kzalloc(airoha_npu_mbox_size(sizeof(*ppe_data)), GFP_KERNEL); if (!ppe_data) return -ENOMEM; @@ -354,7 +361,7 @@ static int airoha_npu_ppe_deinit(struct airoha_npu *npu) struct ppe_mbox_data *ppe_data; int err; - ppe_data = kzalloc_obj(*ppe_data); + ppe_data = kzalloc(airoha_npu_mbox_size(sizeof(*ppe_data)), GFP_KERNEL); if (!ppe_data) return -ENOMEM; @@ -375,7 +382,7 @@ static int airoha_npu_ppe_flush_sram_entries(struct airoha_npu *npu, struct ppe_mbox_data *ppe_data; int err; - ppe_data = kzalloc_obj(*ppe_data); + ppe_data = kzalloc(airoha_npu_mbox_size(sizeof(*ppe_data)), GFP_KERNEL); if (!ppe_data) return -ENOMEM; @@ -399,7 +406,7 @@ static int airoha_npu_foe_commit_entry(struct airoha_npu *npu, struct ppe_mbox_data *ppe_data; int err; - ppe_data = kzalloc_obj(*ppe_data, GFP_ATOMIC); + ppe_data = kzalloc(airoha_npu_mbox_size(sizeof(*ppe_data)), GFP_ATOMIC); if (!ppe_data) return -ENOMEM; @@ -434,7 +441,7 @@ static int airoha_npu_ppe_stats_setup(struct airoha_npu *npu, int err, size = num_stats_entries * sizeof(*npu->stats); struct ppe_mbox_data *ppe_data; - ppe_data = kzalloc_obj(*ppe_data, GFP_ATOMIC); + ppe_data = kzalloc(airoha_npu_mbox_size(sizeof(*ppe_data)), GFP_ATOMIC); if (!ppe_data) return -ENOMEM; @@ -466,7 +473,7 @@ static int airoha_npu_wlan_msg_send(struct airoha_npu *npu, int ifindex, int err, len; len = sizeof(*wlan_data) + data_len; - wlan_data = kzalloc(len, gfp); + wlan_data = kzalloc(airoha_npu_mbox_size(len), gfp); if (!wlan_data) return -ENOMEM; @@ -489,7 +496,7 @@ static int airoha_npu_wlan_msg_get(struct airoha_npu *npu, int ifindex, int err, len; len = sizeof(*wlan_data) + data_len; - wlan_data = kzalloc(len, gfp); + wlan_data = kzalloc(airoha_npu_mbox_size(len), gfp); if (!wlan_data) return -ENOMEM; -- 2.55.0