> Commit 6f884eb87a79 ("net: airoha: Fix DMA direction for NPU mailbox
> buffer") switched airoha_npu_send_msg() to DMA_BIDIRECTIONAL so
> non-coherent CPUs invalidate caches before reading NPU GET responses.
> 
> On EN7581 + MT7996 that change regresses probe: the mailbox completes
> successfully, but WLAN_FUNC_GET_WAIT_NPU_VERSION still reads as 0.0 and
> mt76 never binds NPU offload. Healthy boards report 0.1111.
> 
> airoha_npu_send_msg() is also used from PPE foe_commit under
> spin_lock_bh(), so per-message dma_alloc_coherent(GFP_ATOMIC) is a poor
> fit. Allocate one device-managed coherent bounce buffer per NPU core at
> probe and reuse it under the existing per-core mailbox lock. That also
> keeps the buffer valid if the NPU completes a write after a mailbox
> timeout.
> 
> 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 thin wrapper for SET paths.
> 
> Verified on Quantum Fiber / Gemtek W1700K (EN7581 + MT7996).
> 
> 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/
> Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20260806072601.1815487-1-pawlik.dan@gmail.com/
> Assisted-by: Cursor:composer-2
> Signed-off-by: Daniel Pawlik <pawlik.dan@gmail.com>
> ---
> v4:
> - drop rsp_off; copy trailing reply_len bytes into reply pointer
> - split __airoha_npu_send_msg() + thin airoha_npu_send_msg() wrapper
>   so SET callers stay unchanged
> - fix reverse-christmas-tree local variable ordering
> - constify data argument; clarify reply copy comment
> 
> v3:
> - move coherent mailbox buffer into struct airoha_npu_core (buf/addr)
> - allocate one buffer per core at probe
> - add optional reply buffer to avoid the extra copy in
>   airoha_npu_wlan_msg_get()
> - document AIROHA_NPU_MBOX_SIZE vs ppe_mbox_data / WLAN payloads
> 
> v2:
> - allocate one coherent mailbox buffer at probe and reuse it under the
>   per-core lock instead of per-message dma_alloc_coherent(GFP_ATOMIC)
> 
>  drivers/net/ethernet/airoha/airoha_npu.c  | 70 +++++++++++++++++------
>  include/linux/soc/airoha/airoha_offload.h |  3 +
>  2 files changed, 54 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/ethernet/airoha/airoha_npu.c b/drivers/net/ethernet/airoha/airoha_npu.c
> index b679bed952de..74da3c4d06e4 100644
> --- a/drivers/net/ethernet/airoha/airoha_npu.c
> +++ b/drivers/net/ethernet/airoha/airoha_npu.c
> @@ -23,6 +23,12 @@
>  #define NPU_EN7581_FIRMWARE_RV32_MAX_SIZE	0x200000
>  #define NPU_EN7581_FIRMWARE_DATA_MAX_SIZE	0x10000
>  #define NPU_DUMP_SIZE				512
> +/*
> + * Mailbox DMA payload size. Covers sizeof(struct ppe_mbox_data) (28) and
> + * WLAN TLV messages (header + payload); largest in-tree WLAN payload today
> + * is 16 bytes (INODE_TXRX_REG_ADDR). Keep headroom for future commands.
> + */
> +#define AIROHA_NPU_MBOX_SIZE			256
>  
>  #define REG_NPU_LOCAL_SRAM		0x0
>  
> @@ -160,23 +166,32 @@ 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,
> +				 int reply_len)

if you use an u16 for reply_len you can avoid the reply_len < 0 check below.

>  {
> -	u16 core = 0; /* FIXME */
> -	u32 val, offset = core << 4;
> -	dma_addr_t dma_addr;
> +	struct airoha_npu_core *c = &npu->cores[0]; /* FIXME: core */
> +	u32 val, offset = 0;
>  	int ret;
>  
> -	dma_addr = dma_map_single(npu->dev, p, size, DMA_BIDIRECTIONAL);
> -	ret = dma_mapping_error(npu->dev, dma_addr);
> -	if (ret)
> -		return ret;
> +	if (len > AIROHA_NPU_MBOX_SIZE ||
> +	    (reply && (reply_len < 0 || reply_len > len)))

maybe you can have a dedicated if for this check

	if (reply && reply_len > len)
		reutrn -EINVAL;

> +		return -EINVAL;
>  
> -	spin_lock_bh(&npu->cores[core].lock);
> +	/*
> +	 * Mailbox payloads are bidirectional (CPU request, NPU response).
> +	 * On EN7581+MT7996, streaming DMA_BIDIRECTIONAL against the
> +	 * caller kzalloc() buffer can leave WLAN_FUNC_GET_WAIT_NPU_VERSION
> +	 * reading as 0.0 despite MBOX success. Reuse a probe-time coherent
> +	 * bounce buffer under the per-core lock (also used from PPE
> +	 * foe_commit under atomic context).
> +	 */
> +	spin_lock_bh(&c->lock);
> +
> +	memcpy(c->buf, data, len);
>  
> -	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(0) + offset, c->addr);
> +	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 +204,21 @@ 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);
> +	/* Copy the trailing reply_len bytes of the response. */
> +	if (!ret && reply)
> +		memcpy(reply, c->buf + len - reply_len, reply_len);
>  
> -	dma_unmap_single(npu->dev, dma_addr, size, DMA_BIDIRECTIONAL);
> +	spin_unlock_bh(&c->lock);
>  
>  	return ret;
>  }
>  
> +static inline int airoha_npu_send_msg(struct airoha_npu *npu, int func_id,
> +				      const void *data, int len)
> +{

if you put in .c file please drop the inline.

> +	return __airoha_npu_send_msg(npu, func_id, data, len, NULL, 0);
> +}
> +
>  static int airoha_npu_load_firmware(struct device *dev, void __iomem *addr,
>  				    const char *fw_name, int fw_max_size)
>  {
> @@ -442,8 +465,9 @@ static int airoha_npu_ppe_stats_setup(struct airoha_npu *npu,
>  	ppe_data->func_id = PPE_FUNC_SET_WAIT_FLOW_STATS_SETUP;
>  	ppe_data->stats_info.foe_stats_addr = foe_stats_addr;
>  
> -	err = airoha_npu_send_msg(npu, NPU_FUNC_PPE, ppe_data,
> -				  sizeof(*ppe_data));
> +	err = __airoha_npu_send_msg(npu, NPU_FUNC_PPE, ppe_data,
> +				    sizeof(*ppe_data), ppe_data,
> +				    sizeof(*ppe_data));

why not using airoha_npu_send_msg() here?

Regards,
Lorenzo

>  	if (err)
>  		goto out;
>  
> @@ -497,9 +521,8 @@ 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 +793,15 @@ 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];
> +
> +		core->buf = dmam_alloc_coherent(dev, AIROHA_NPU_MBOX_SIZE,
> +						&core->addr, GFP_KERNEL);
> +		if (!core->buf)
> +			return -ENOMEM;
> +	}
> +
>  	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..16a988ad7467 100644
> --- a/include/linux/soc/airoha/airoha_offload.h
> +++ b/include/linux/soc/airoha/airoha_offload.h
> @@ -173,6 +173,9 @@ struct airoha_npu {
>  		/* protect concurrent npu memory accesses */
>  		spinlock_t lock;
>  		struct work_struct wdt_work;
> +		/* Coherent bounce buffer for mailbox cmd/rsp */
> +		void *buf;
> +		dma_addr_t addr;
>  	} cores[NPU_NUM_CORES];
>  
>  	int irqs[NPU_NUM_IRQ];
> -- 
> 2.55.0
>