All the tables of NETC switch are managed through the command BD ring,
but unlike ENETC, the switch has two command BD rings, if the current
ring is busy, the switch driver can switch to another ring to manage
the table. Currently, the NTMP driver does not support multiple rings.
Therefore, netc_select_cbdr() is added to select a appropriate ring to
execute the command for the switch.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
 drivers/net/ethernet/freescale/enetc/ntmp.c | 27 ++++++++++++++++++---
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/ntmp.c b/drivers/net/ethernet/freescale/enetc/ntmp.c
index 9fc3422137fc..e23a32946762 100644
--- a/drivers/net/ethernet/freescale/enetc/ntmp.c
+++ b/drivers/net/ethernet/freescale/enetc/ntmp.c
@@ -117,6 +117,25 @@ static void ntmp_clean_cbdr(struct netc_cbdr *cbdr)
 	cbdr->next_to_clean = i;
 }
 
+static struct netc_cbdr *netc_select_cbdr(struct ntmp_user *user)
+{
+	int cpu, i;
+
+	for (i = 0; i < user->cbdr_num; i++) {
+		if (spin_is_locked(&user->ring[i].ring_lock))
+			continue;
+
+		return &user->ring[i];
+	}
+
+	/* If all the command BDRs are busy now, we select
+	 * one of them, but need to wait for a while to use.
+	 */
+	cpu = smp_processor_id();
+
+	return &user->ring[cpu % user->cbdr_num];
+}
+
 static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
 {
 	union netc_cbd *cur_cbd;
@@ -125,10 +144,10 @@ static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
 	u16 status;
 	u32 val;
 
-	/* Currently only i.MX95 ENETC is supported, and it only has one
-	 * command BD ring
-	 */
-	cbdr = &user->ring[0];
+	if (user->cbdr_num == 1)
+		cbdr = &user->ring[0];
+	else
+		cbdr = netc_select_cbdr(user);
 
 	spin_lock_bh(&cbdr->ring_lock);
 
-- 
2.34.1

From: Frank Li (AI-BOT) <frank.li@nxp.com>

> +static struct netc_cbdr *netc_select_cbdr(struct ntmp_user *user)
> +{
> +	int cpu, i;
> +
> +	for (i = 0; i < user->cbdr_num; i++) {
> +		if (spin_is_locked(&user->ring[i].ring_lock))
> +			continue;
> +
> +		return &user->ring[i];
> +	}
> +
> +	/* If all the command BDRs are busy now, we select
> +	 * one of them, but need to wait for a while to use.
> +	 */
> +	cpu = smp_processor_id();
> +
> +	return &user->ring[cpu % user->cbdr_num];
> +}

AI: spin_is_locked() is not reliable for lockless checks on all architectures.
Consider using spin_trylock() instead, or document why this racy check isi
acceptable here.

> +	if (user->cbdr_num == 1)
> +		cbdr = &user->ring[0];
> +	else
> +		cbdr = netc_select_cbdr(user);

AI: The special case for cbdr_num == 1 is redundant; netc_select_cbdr() handles
it correctly. Simplify to: cbdr = netc_select_cbdr(user);

Need owner do futher judgement

Frank

This is an AI-generated review of your patch. The human sending this
email has considered the AI review valid, or at least plausible.

For local reproduction steps see https://netdev-ai.bots.linux.dev/ai-local.html
---
net: enetc: add multiple command BD rings support

This commit adds support for multiple command BD rings in the NTMP
driver. When the NETC switch has multiple command BD rings and one is
busy, the driver can select an alternate ring to execute commands.

> diff --git a/drivers/net/ethernet/freescale/enetc/ntmp.c b/drivers/net/ethernet/freescale/enetc/ntmp.c
> index 9fc3422137fc..e23a32946762 100644
> --- a/drivers/net/ethernet/freescale/enetc/ntmp.c
> +++ b/drivers/net/ethernet/freescale/enetc/ntmp.c
> @@ -117,6 +117,25 @@ static void ntmp_clean_cbdr(struct netc_cbdr *cbdr)
>  	cbdr->next_to_clean = i;
>  }
>
> +static struct netc_cbdr *netc_select_cbdr(struct ntmp_user *user)
> +{
> +	int cpu, i;
> +
> +	for (i = 0; i < user->cbdr_num; i++) {
> +		if (spin_is_locked(&user->ring[i].ring_lock))
> +			continue;
> +
> +		return &user->ring[i];
> +	}
> +
> +	/* If all the command BDRs are busy now, we select
> +	 * one of them, but need to wait for a while to use.
> +	 */
> +	cpu = smp_processor_id();
> +
> +	return &user->ring[cpu % user->cbdr_num];
> +}
> +

Can this trigger a preemption warning? netc_select_cbdr() is called from
netc_xmit_ntmp_cmd() before spin_lock_bh() is acquired, and the callers
(ntmp_maft_add_entry, ntmp_fdbt_add_entry, etc.) run in process context
with preemption enabled.

Using smp_processor_id() in preemptible code triggers a
"BUG: using smp_processor_id() in preemptible code" warning under
CONFIG_DEBUG_PREEMPT.

Since the CPU value here is only used as a hint for ring selection and not
for correctness, would raw_smp_processor_id() be more appropriate?

>  static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
>  {
>  	union netc_cbd *cur_cbd;
> @@ -125,10 +144,10 @@ static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
>  	u16 status;
>  	u32 val;
>
> -	/* Currently only i.MX95 ENETC is supported, and it only has one
> -	 * command BD ring
> -	 */
> -	cbdr = &user->ring[0];
> +	if (user->cbdr_num == 1)
> +		cbdr = &user->ring[0];
> +	else
> +		cbdr = netc_select_cbdr(user);
>
>  	spin_lock_bh(&cbdr->ring_lock);