Re: [PATCH v6 net-next 13/15] net: dsa: netc: initialize buffer pool table and implement flow-control

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The IPV-to-buffer-pool mapping algorithm fails when a port is allocated more than 8 buffer pools, silently routing all traffic to a single pool.
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commit 0b5e4aba36a49ce1de9eb84ec706f482331550cf
Author: Wei Fang <wei.fang@nxp.com>

net: dsa: netc: initialize buffer pool table and implement flow-control

This commit initializes the buffer pool table and implements flow control
for the NXP netc DSA driver. It adds logic to dynamically map the 8 internal
priority values (IPVs) to the available buffer pools per port based on
hardware capabilities.

> diff --git a/drivers/net/dsa/netc/netc_main.c b/drivers/net/dsa/netc/netc_main.c
> --- a/drivers/net/dsa/netc/netc_main.c
> +++ b/drivers/net/dsa/netc/netc_main.c

[ ... ]

> +static void netc_ipv_to_buffer_pool_mapping(struct netc_switch *priv)
> +{
> +	int bp_per_port = priv->num_bp / priv->info->num_ports;
> +	int q = NETC_IPV_NUM / bp_per_port;
> +	int r = NETC_IPV_NUM % bp_per_port;
> +	int num = q + r;
> +
> +	/* IPV-to–buffer-pool mapping per port:
> +	 * Each port is allocated 'bp_per_port' buffer pools and supports 8
> +	 * IPVs, where a higher IPV indicates a higher frame priority. Each
> +	 * IPV can be mapped to only one buffer pool.
> +	 *
> +	 * The mapping rule is as follows:
> +	 * - The first 'num' IPVs share the port's first buffer pool (index
> +	 * 'base_id').
> +	 * - After that, every 'q' IPVs share one buffer pool, with pool
> +	 * indices increasing sequentially.
> +	 */
> +	for (int i = 0; i < priv->info->num_ports; i++) {
> +		u32 base_id = i * bp_per_port;
> +		u32 bp_id = base_id;
> +		u64 mapping = 0;
> +
> +		for (int ipv = 0; ipv < NETC_IPV_NUM; ipv++) {
> +			/* Update the buffer pool index */
> +			if (ipv >= num)
> +				bp_id = base_id + ((ipv - num) / q) + 1;

What happens if a future hardware revision allocates more than 8 buffer pools
per port?

If bp_per_port is greater than NETC_IPV_NUM (8), q evaluates to 0 and num
evaluates to 8.

Because ipv loops from 0 to 7, the condition ipv >= num will never be true.
As a result, all 8 traffic priorities would be mapped to a single buffer pool
(base_id), leaving the remaining pools unused instead of maximizing
utilization.

Should bp_per_port be clamped to NETC_IPV_NUM before calculating q to
prevent this?

> +
> +			mapping |= (u64)bp_id << (ipv * 8);
> +		}
> +
> +		netc_port_set_pbpmcr(priv->ports[i], mapping);
> +	}
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260509102954.4116624-1-wei.fang@nxp.com?part=13