net: sparx5: fix source port register when mirroring

When port mirroring is added to a port, the bit position of the source
port, needs to be written to the register ANA_AC_PROBE_PORT_CFG.  This
register is replicated for n_ports > 32, and therefore we need to derive
the correct register from the port number.

Before this patch, we wrongly calculate the register from portno /
BITS_PER_BYTE, where the divisor ought to be 32, causing any port >=8 to
be written to the wrong register. We fix this, by using do_div(), where
the dividend is the register, the remainder is the bit position and the
divisor is now 32.

Fixes: 4e50d72b ("net: sparx5: add port mirroring implementation")
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241009-mirroring-fix-v1-1-9ec962301989@microchip.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microchip/sparx5/sparx5_mirror.c

@@ -31,10 +31,10 @@ static u64 sparx5_mirror_port_get(struct sparx5 *sparx5, u32 idx)
 /* Add port to mirror (only front ports) */
 static void sparx5_mirror_port_add(struct sparx5 *sparx5, u32 idx, u32 portno)
 {
-	u32 val, reg = portno;
+	u64 reg = portno;
+	u32 val;
 
-	reg = portno / BITS_PER_BYTE;
-	val = BIT(portno % BITS_PER_BYTE);
+	val = BIT(do_div(reg, 32));
 
 	if (reg == 0)
 		return spx5_rmw(val, val, sparx5, ANA_AC_PROBE_PORT_CFG(idx));
@@ -45,10 +45,10 @@ static void sparx5_mirror_port_add(struct sparx5 *sparx5, u32 idx, u32 portno)
 /* Delete port from mirror (only front ports) */
 static void sparx5_mirror_port_del(struct sparx5 *sparx5, u32 idx, u32 portno)
 {
-	u32 val, reg = portno;
+	u64 reg = portno;
+	u32 val;
 
-	reg = portno / BITS_PER_BYTE;
-	val = BIT(portno % BITS_PER_BYTE);
+	val = BIT(do_div(reg, 32));
 
 	if (reg == 0)
 		return spx5_rmw(0, val, sparx5, ANA_AC_PROBE_PORT_CFG(idx));