The SF2 crossbar register is a packed bitfield, giving the index of the
external port selected for each of the internal ports. On BCM4908 (the
only currently-supported switch family with a crossbar), there are 2
internal ports and 3 external ports, so there are 2 bits per internal
port.

The driver currently conflates the "bits per port" and "number of ports"
concepts, lumping both into the `num_crossbar_int_ports` field. Since it
is currently only possible for either of these counts to have a value of
2, there is no behavioral error resulting from this situation for now.

Make the code more readable (and support the future possibility of
larger crossbars) by adding a `num_crossbar_ext_bits` field to represent
the "bits per port" count and relying on this where appropriate instead.

Signed-off-by: Sam Edwards <CFSworks@gmail.com>
---
 drivers/net/dsa/bcm_sf2.c | 9 ++++++---
 drivers/net/dsa/bcm_sf2.h | 1 +
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/dsa/bcm_sf2.c b/drivers/net/dsa/bcm_sf2.c
index 0e663ec0c12a..3ae794a30ace 100644
--- a/drivers/net/dsa/bcm_sf2.c
+++ b/drivers/net/dsa/bcm_sf2.c
@@ -513,12 +513,12 @@ static void bcm_sf2_crossbar_setup(struct bcm_sf2_priv *priv)
 	u32 reg;
 	int i;
 
-	mask = BIT(priv->num_crossbar_int_ports) - 1;
+	mask = BIT(priv->num_crossbar_ext_bits) - 1;
 
 	reg = reg_readl(priv, REG_CROSSBAR);
 	switch (priv->type) {
 	case BCM4908_DEVICE_ID:
-		shift = CROSSBAR_BCM4908_INT_P7 * priv->num_crossbar_int_ports;
+		shift = CROSSBAR_BCM4908_INT_P7 * priv->num_crossbar_ext_bits;
 		reg &= ~(mask << shift);
 		if (0) /* FIXME */
 			reg |= CROSSBAR_BCM4908_EXT_SERDES << shift;
@@ -536,7 +536,7 @@ static void bcm_sf2_crossbar_setup(struct bcm_sf2_priv *priv)
 
 	reg = reg_readl(priv, REG_CROSSBAR);
 	for (i = 0; i < priv->num_crossbar_int_ports; i++) {
-		shift = i * priv->num_crossbar_int_ports;
+		shift = i * priv->num_crossbar_ext_bits;
 
 		dev_dbg(dev, "crossbar int port #%d - ext port #%d\n", i,
 			(reg >> shift) & mask);
@@ -1260,6 +1260,7 @@ struct bcm_sf2_of_data {
 	unsigned int core_reg_align;
 	unsigned int num_cfp_rules;
 	unsigned int num_crossbar_int_ports;
+	unsigned int num_crossbar_ext_bits;
 };
 
 static const u16 bcm_sf2_4908_reg_offsets[] = {
@@ -1288,6 +1289,7 @@ static const struct bcm_sf2_of_data bcm_sf2_4908_data = {
 	.reg_offsets	= bcm_sf2_4908_reg_offsets,
 	.num_cfp_rules	= 256,
 	.num_crossbar_int_ports = 2,
+	.num_crossbar_ext_bits = 2,
 };
 
 /* Register offsets for the SWITCH_REG_* block */
@@ -1399,6 +1401,7 @@ static int bcm_sf2_sw_probe(struct platform_device *pdev)
 	priv->core_reg_align = data->core_reg_align;
 	priv->num_cfp_rules = data->num_cfp_rules;
 	priv->num_crossbar_int_ports = data->num_crossbar_int_ports;
+	priv->num_crossbar_ext_bits = data->num_crossbar_ext_bits;
 
 	priv->rcdev = devm_reset_control_get_optional_exclusive(&pdev->dev,
 								"switch");
diff --git a/drivers/net/dsa/bcm_sf2.h b/drivers/net/dsa/bcm_sf2.h
index f95f4880b69e..4fda075a3449 100644
--- a/drivers/net/dsa/bcm_sf2.h
+++ b/drivers/net/dsa/bcm_sf2.h
@@ -75,6 +75,7 @@ struct bcm_sf2_priv {
 	unsigned int			core_reg_align;
 	unsigned int			num_cfp_rules;
 	unsigned int			num_crossbar_int_ports;
+	unsigned int			num_crossbar_ext_bits;
 
 	/* spinlock protecting access to the indirect registers */
 	spinlock_t			indir_lock;
-- 
2.44.2

On 10/3/24 14:23, Sam Edwards wrote:
> The SF2 crossbar register is a packed bitfield, giving the index of the
> external port selected for each of the internal ports. On BCM4908 (the
> only currently-supported switch family with a crossbar), there are 2
> internal ports and 3 external ports, so there are 2 bits per internal
> port.
> 
> The driver currently conflates the "bits per port" and "number of ports"
> concepts, lumping both into the `num_crossbar_int_ports` field. Since it
> is currently only possible for either of these counts to have a value of
> 2, there is no behavioral error resulting from this situation for now.
> 
> Make the code more readable (and support the future possibility of
> larger crossbars) by adding a `num_crossbar_ext_bits` field to represent
> the "bits per port" count and relying on this where appropriate instead.
> 
> Signed-off-by: Sam Edwards <CFSworks@gmail.com>

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
-- 
Florian