RE: [PATCH v2 net-next 13/14] net: dsa: netc: initialize buffer bool table and implement flow-control

quoted

+static u32 netc_get_buffer_pool_num(struct netc_switch *priv)
+{
+	return netc_base_rd(&priv->regs, NETC_BPCAPR) & BPCAPR_NUM_BP;
+}
+
+static void netc_port_set_pbpmcr(struct netc_port *np, u64 mapping)
+{
+	u32 pbpmcr0 = lower_32_bits(mapping);
+	u32 pbpmcr1 = upper_32_bits(mapping);
+
+	netc_port_wr(np, NETC_PBPMCR0, pbpmcr0);
+	netc_port_wr(np, NETC_PBPMCR1, pbpmcr1);
+}
+
+static void netc_ipv_to_buffer_pool_mapping(struct netc_switch *priv)
+{
+	int num_port_bp = priv->num_bp / priv->info->num_ports;
+	int q = NETC_IPV_NUM / num_port_bp;
               ^^^^

Can this cause a division by zero?  If netc_get_buffer_pool_num() reads

From hardware perspective, num_bp is more than num_ports, so num_port_bp
will not be zero. Let me think how to improve it to avoid such false positive.

the hardware register NETC_BPCAPR and returns 0, then num_port_bp would
be
0 and this division would crash the kernel.

The call chain is:

netc_setup()
  netc_switch_bpt_default_config()
    priv->num_bp = netc_get_buffer_pool_num()
    netc_ipv_to_buffer_pool_mapping()
      num_port_bp = priv->num_bp / priv->info->num_ports;
      q = NETC_IPV_NUM / num_port_bp;  <- division by zero

Should netc_switch_bpt_default_config() validate that priv->num_bp is
non-zero before proceeding?

quoted

+	int r = NETC_IPV_NUM % num_port_bp;
+	int num = q + r;
+
+	/* IPV-to-buffer-pool mapping per port:

[ ... ]

quoted

+static int netc_switch_bpt_default_config(struct netc_switch *priv)
+{
+	priv->num_bp = netc_get_buffer_pool_num(priv);
+	priv->bpt_list = devm_kcalloc(priv->dev, priv->num_bp,
+				      sizeof(struct bpt_cfge_data),
+				      GFP_KERNEL);
+	if (!priv->bpt_list)
+		return -ENOMEM;
+
+	/* Initialize the maximum threshold of each buffer pool entry */
+	for (int i = 0; i < priv->num_bp; i++) {
+		struct bpt_cfge_data *cfge = &priv->bpt_list[i];
+		int err;
+
+		cfge->max_thresh = cpu_to_le16(NETC_BP_THRESH);
+		err = ntmp_bpt_update_entry(&priv->ntmp, i, cfge);
+		if (err)
+			return err;
+	}
+
+	netc_ipv_to_buffer_pool_mapping(priv);
+
+	return 0;
+}
+

[ ... ]

quoted

@@ -1224,6 +1313,40 @@ static void netc_port_set_hd_flow_control(struct

netc_port *np, bool en)

quoted

 			  en ? PM_CMD_CFG_HD_FCEN : 0);
 }

+static void netc_port_set_tx_pause(struct netc_port *np, bool tx_pause)
+{
+	struct netc_switch *priv = np->switch_priv;
+	int port = np->dp->index;
+	int i, j, num_bp;
+
+	num_bp = priv->num_bp / priv->info->num_ports;
+	for (i = 0, j = port * num_bp; i < num_bp; i++, j++) {
+		struct bpt_cfge_data *cfge;
+
+		cfge = &priv->bpt_list[j];
+		if (tx_pause) {
+			cfge->fc_on_thresh = cpu_to_le16(NETC_FC_THRESH_ON);
+			cfge->fc_off_thresh = cpu_to_le16(NETC_FC_THRESH_OFF);
+			cfge->fccfg_sbpen = FIELD_PREP(BPT_FC_CFG,
+						       BPT_FC_CFG_EN_BPFC);
+			cfge->fc_ports = cpu_to_le32(BIT(port));
+		} else {
+			cfge->fc_on_thresh = cpu_to_le16(0);
+			cfge->fc_off_thresh = cpu_to_le16(0);
+			cfge->fccfg_sbpen = 0;
+			cfge->fc_ports = cpu_to_le32(0);
+		}
+
+		ntmp_bpt_update_entry(&priv->ntmp, j, cfge);
                ^^^^

Should the return value of ntmp_bpt_update_entry() be checked here?

Simon Horman noted in v1 review that other NTMP table operations in the
driver propagate errors from the update functions. While this was fixed
in netc_switch_bpt_default_config() in v2, the same issue remains here.

If the hardware update fails (for example, DMA allocation failure or
hardware timeout), the driver's bpt_list will have flow control values that
do not match the actual hardware state, potentially causing incorrect flow
control behavior.

Okay, I will improve it.