Re: [PATCH net-next v4 08/13] net: wwan: t7xx: Add data path interface

On 2/8/2022 12:19 AM, Ilpo Järvinen wrote:

On Thu, 13 Jan 2022, Ricardo Martinez wrote:

quoted

From: Haijun Liu <haijun.liu@mediatek.com>

Data Path Modem AP Interface (DPMAIF) HIF layer provides methods
for initialization, ISR, control and event handling of TX/RX flows.

...

quoted

+	spin_lock_irqsave(&txq->tx_lock, flags);
+	cur_idx = txq->drb_wr_idx;
+	drb_wr_idx_backup = cur_idx;
+
+	txq->drb_wr_idx += send_cnt;
+	if (txq->drb_wr_idx >= txq->drb_size_cnt)
+		txq->drb_wr_idx -= txq->drb_size_cnt;
+
+	t7xx_setup_msg_drb(dpmaif_ctrl, txq->index, cur_idx, skb->len, 0, skb->cb[TX_CB_NETIF_IDX]);
+	t7xx_record_drb_skb(dpmaif_ctrl, txq->index, cur_idx, skb, 1, 0, 0, 0, 0);
+	spin_unlock_irqrestore(&txq->tx_lock, flags);
+
+	cur_idx = t7xx_ring_buf_get_next_wr_idx(txq->drb_size_cnt, cur_idx);
+
+	for (wr_cnt = 0; wr_cnt < payload_cnt; wr_cnt++) {
+		if (!wr_cnt) {
+			data_len = skb_headlen(skb);
+			data_addr = skb->data;
+			is_frag = false;
+		} else {
+			skb_frag_t *frag = info->frags + wr_cnt - 1;
+
+			data_len = skb_frag_size(frag);
+			data_addr = skb_frag_address(frag);
+			is_frag = true;
+		}
+
+		if (wr_cnt == payload_cnt - 1)
+			is_last_one = true;
+
+		/* TX mapping */
+		bus_addr = dma_map_single(dpmaif_ctrl->dev, data_addr, data_len, DMA_TO_DEVICE);
+		if (dma_mapping_error(dpmaif_ctrl->dev, bus_addr)) {
+			dev_err(dpmaif_ctrl->dev, "DMA mapping fail\n");
+			atomic_set(&txq->tx_processing, 0);
+
+			spin_lock_irqsave(&txq->tx_lock, flags);
+			txq->drb_wr_idx = drb_wr_idx_backup;
+			spin_unlock_irqrestore(&txq->tx_lock, flags);

Hmm, can txq's drb_wr_idx get updated (or cleared) by something else
in between these critical sections?

drb_wr_idx cannot be modified inbetween, but it can be used to calculate the number of DRBs available, which shouldn't be a problem.
The function is reserving the DRBs at the beginning, in the rare case of error it will release them.
...

+		txq_id = t7xx_select_tx_queue(dpmaif_ctrl);
+		if (txq_id >= 0) {
t7xx_select_tx_queue used to do que_started check (in v2) but it
doesn't anymore so this if is always true these days. I'm left to
wonder though if it was ok to drop that que_started check?

The que_started check wasn't supposed to be dropped, I'll add it back.

...

quoted

+/* SKB control buffer indexed values */
+#define TX_CB_NETIF_IDX		0
+#define TX_CB_QTYPE		1
+#define TX_CB_DRB_CNT		2

The normal way of storing a struct to skb->cb area is:

struct t7xx_skb_cb {
	u8	netif_idx;
	u8	qtype;
	u8	drb_cnt;
};

#define T7XX_SKB_CB(__skb)	((struct t7xx_skb_cb *)&((__skb)->cb[0]))

However, there's only a single txqt/qtype (TXQ_TYPE_DEFAULT) in the
patchset? And it seems to me that drb_cnt is a value that could be always
derived using t7xx_get_drb_cnt_per_skb() from the skb rather than
stored?

The next iteration will contain t7xx_tx_skb_cb and t7xx_rx_skb_cb structures.

Also, q_number is going to be used instead of qtype.

Only one queue is used but I think we can keep this code generic as it is straight forward (not like the drb_lack case), any thoughts?

quoted

+#define DRB_PD_DATA_LEN		((u32)GENMASK(31, 16))

Drop the cast?

The cast was added to avoid a compiler warning about truncated bits.

I'll move it to the place where it is required:

drb->header &= cpu_to_le32(~(u32)DRB_PD_DATA_LEN);

...