[PATCH v7] net: airoha: npu: use aligned streaming DMA for mailbox messages

[Daniel Pawlik <pawlik.dan@gmail.com>]

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.

Bounce mailbox traffic through a per-core cacheline-aligned buffer
allocated at probe. Map ALIGN(len, SMP_CACHE_BYTES) with
DMA_BIDIRECTIONAL while programming the original payload length into the
mailbox length register. Copy the reply only after dma_unmap_single() so
the CPU sees the NPU-written payload on non-coherent DMA.

Introduce __airoha_npu_send_msg() with an optional reply pointer so GET
callers can copy the trailing response payload once. Keep
airoha_npu_send_msg() as a wrapper that copies the full response back
into the caller buffer, matching the old bidirectional mapping.

Tested on Quantum Fiber / Gemtek W1700K (EN7581 + MT7996), kernel
6.18.44, including two cold reboots and sustained WiFi use.

Fixes: 6f884eb87a79 ("net: airoha: Fix DMA direction for NPU mailbox buffer")
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20260805070851.2885888-1-pawlik.dan@gmail.com/
Assisted-by: Cursor:composer-2
Signed-off-by: Daniel Pawlik <pawlik.dan@gmail.com>
---
 drivers/net/ethernet/airoha/airoha_npu.c  | 62 ++++++++++++++++++-----
 include/linux/soc/airoha/airoha_offload.h |  1 +
 2 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/airoha/airoha_npu.c b/drivers/net/ethernet/airoha/airoha_npu.c
index b679bed952de..2ba78bf0e97b 100644
--- a/drivers/net/ethernet/airoha/airoha_npu.c
+++ b/drivers/net/ethernet/airoha/airoha_npu.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/devcoredump.h>
+#include <linux/dma-mapping.h>
 #include <linux/firmware.h>
 #include <linux/platform_device.h>
 #include <linux/of_net.h>
@@ -23,6 +24,8 @@
 #define NPU_EN7581_FIRMWARE_RV32_MAX_SIZE	0x200000
 #define NPU_EN7581_FIRMWARE_DATA_MAX_SIZE	0x10000
 #define NPU_DUMP_SIZE				512
+/* Maximum mailbox DMA payload (PPE ~28 bytes, WLAN TLV up to 24). */
+#define AIROHA_NPU_MBOX_SIZE			256
 
 #define REG_NPU_LOCAL_SRAM		0x0
 
@@ -160,23 +163,33 @@ struct wlan_mbox_data {
 	DECLARE_FLEX_ARRAY(u8, d);
 };
 
-static int airoha_npu_send_msg(struct airoha_npu *npu, int func_id,
-			       void *p, int size)
+static int __airoha_npu_send_msg(struct airoha_npu *npu, int func_id,
+				 const void *data, int len, void *reply,
+				 u16 reply_len)
 {
-	u16 core = 0; /* FIXME */
-	u32 val, offset = core << 4;
+	struct airoha_npu_core *core = &npu->cores[0]; /* FIXME: core */
 	dma_addr_t dma_addr;
+	unsigned int map_len = ALIGN(len, SMP_CACHE_BYTES);
+	u32 val, offset = 0;
 	int ret;
 
-	dma_addr = dma_map_single(npu->dev, p, size, DMA_BIDIRECTIONAL);
+	if (len <= 0 || len > AIROHA_NPU_MBOX_SIZE)
+		return -EINVAL;
+
+	if (reply && reply_len > len)
+		return -EINVAL;
+
+	spin_lock_bh(&core->lock);
+
+	memcpy(core->buf, data, len);
+
+	dma_addr = dma_map_single(npu->dev, core->buf, map_len, DMA_BIDIRECTIONAL);
 	ret = dma_mapping_error(npu->dev, dma_addr);
 	if (ret)
-		return ret;
-
-	spin_lock_bh(&npu->cores[core].lock);
+		goto unlock;
 
 	regmap_write(npu->regmap, REG_CR_MBQ0_CTRL(0) + offset, dma_addr);
-	regmap_write(npu->regmap, REG_CR_MBQ0_CTRL(1) + offset, size);
+	regmap_write(npu->regmap, REG_CR_MBQ0_CTRL(1) + offset, len);
 	regmap_read(npu->regmap, REG_CR_MBQ0_CTRL(2) + offset, &val);
 	regmap_write(npu->regmap, REG_CR_MBQ0_CTRL(2) + offset, val + 1);
 	val = FIELD_PREP(MBOX_MSG_FUNC_ID, func_id) | MBOX_MSG_WAIT_RSP;
@@ -189,13 +202,23 @@ static int airoha_npu_send_msg(struct airoha_npu *npu, int func_id,
 	if (!ret && FIELD_GET(MBOX_MSG_STATUS, val) != NPU_MBOX_SUCCESS)
 		ret = -EINVAL;
 
-	spin_unlock_bh(&npu->cores[core].lock);
+	dma_unmap_single(npu->dev, dma_addr, map_len, DMA_BIDIRECTIONAL);
 
-	dma_unmap_single(npu->dev, dma_addr, size, DMA_BIDIRECTIONAL);
+	/* Copy the trailing reply_len bytes of the response. */
+	if (!ret && reply)
+		memcpy(reply, core->buf + len - reply_len, reply_len);
+unlock:
+	spin_unlock_bh(&core->lock);
 
 	return ret;
 }
 
+static int airoha_npu_send_msg(struct airoha_npu *npu, int func_id,
+			       void *data, int len)
+{
+	return __airoha_npu_send_msg(npu, func_id, data, len, data, len);
+}
+
 static int airoha_npu_load_firmware(struct device *dev, void __iomem *addr,
 				    const char *fw_name, int fw_max_size)
 {
@@ -497,9 +520,8 @@ static int airoha_npu_wlan_msg_get(struct airoha_npu *npu, int ifindex,
 	wlan_data->func_type = NPU_OP_GET;
 	wlan_data->func_id = func_id;
 
-	err = airoha_npu_send_msg(npu, NPU_FUNC_WIFI, wlan_data, len);
-	if (!err)
-		memcpy(data, wlan_data->d, data_len);
+	err = __airoha_npu_send_msg(npu, NPU_FUNC_WIFI, wlan_data, len,
+				    data, data_len);
 	kfree(wlan_data);
 
 	return err;
@@ -770,6 +792,18 @@ static int airoha_npu_probe(struct platform_device *pdev)
 	if (err)
 		return err;
 
+	for (i = 0; i < ARRAY_SIZE(npu->cores); i++) {
+		struct airoha_npu_core *core = &npu->cores[i];
+		void *raw;
+
+		raw = devm_kmalloc(dev, AIROHA_NPU_MBOX_SIZE + SMP_CACHE_BYTES,
+				   GFP_KERNEL);
+		if (!raw)
+			return -ENOMEM;
+
+		core->buf = PTR_ALIGN(raw, SMP_CACHE_BYTES);
+	}
+
 	err = airoha_npu_run_firmware(dev, base, &res);
 	if (err)
 		return dev_err_probe(dev, err, "failed to run npu firmware\n");
diff --git a/include/linux/soc/airoha/airoha_offload.h b/include/linux/soc/airoha/airoha_offload.h
index 7589fccfeef6..f635766e3dba 100644
--- a/include/linux/soc/airoha/airoha_offload.h
+++ b/include/linux/soc/airoha/airoha_offload.h
@@ -173,6 +173,7 @@ struct airoha_npu {
 		/* protect concurrent npu memory accesses */
 		spinlock_t lock;
 		struct work_struct wdt_work;
+		void *buf; /* mailbox DMA bounce buffer */
 	} cores[NPU_NUM_CORES];
 
 	int irqs[NPU_NUM_IRQ];
-- 
2.55.0