Re: [PATCH net-next 2/2] net: dsa: mv88e6xxx: Only allow LAG offload on supported hardware

On Fri, Jan 15, 2021 at 01:15:23PM +0200, Vladimir Oltean wrote:

On Fri, Jan 15, 2021 at 11:58:34AM +0100, Tobias Waldekranz wrote:

quoted

There are chips that do have Global 2 registers, and therefore trunk

                       ~~
                       do not

quoted

mapping/mask tables are not available. Additionally Global 2 register
support is build-time optional, so we have to make sure that it is
compiled in.

Fixes: 57e661aae6a8 ("net: dsa: mv88e6xxx: Link aggregation support")
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 4 ++++
 drivers/net/dsa/mv88e6xxx/chip.h | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index dcb1726b68cc..c48d166c2a70 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c

@@ -5385,9 +5385,13 @@ static bool mv88e6xxx_lag_can_offload(struct dsa_switch *ds,
 				      struct net_device *lag,
 				      struct netdev_lag_upper_info *info)
 {
+	struct mv88e6xxx_chip *chip = ds->priv;
 	struct dsa_port *dp;
 	int id, members = 0;
 
+	if (!mv88e6xxx_has_lag(chip))
+		return false;
+
 	id = dsa_lag_id(ds->dst, lag);
 	if (id < 0 || id >= ds->num_lag_ids)
 		return false;

diff --git a/drivers/net/dsa/mv88e6xxx/chip.h b/drivers/net/dsa/mv88e6xxx/chip.h
index 3543055bcb51..333b4fab5aa2 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.h
+++ b/drivers/net/dsa/mv88e6xxx/chip.h

@@ -662,6 +662,15 @@ static inline bool mv88e6xxx_has_pvt(struct mv88e6xxx_chip *chip)
 	return chip->info->pvt;
 }
 
+static inline bool mv88e6xxx_has_lag(struct mv88e6xxx_chip *chip)
+{
+#if (defined(CONFIG_NET_DSA_MV88E6XXX_GLOBAL2))
+	return chip->info->global2_addr != 0;
+#else
+	return false;
+#endif
+}
+

Should we also report ds->num_lag_ids = 0 if !mv88e6xxx_has_lag()?

quoted

 static inline unsigned int mv88e6xxx_num_databases(struct mv88e6xxx_chip *chip)
 {
 	return chip->info->num_databases;
-- 
2.17.1

Actually in mv88e6xxx_detect there is this:

	err = mv88e6xxx_g2_require(chip);
	if (err)
		return err;


#else /* !CONFIG_NET_DSA_MV88E6XXX_GLOBAL2 */

static inline int mv88e6xxx_g2_require(struct mv88e6xxx_chip *chip)
{
	if (chip->info->global2_addr) {
		dev_err(chip->dev, "this chip requires CONFIG_NET_DSA_MV88E6XXX_GLOBAL2 enabled\n");
		return -EOPNOTSUPP;
	}

	return 0;
}

#endif

So CONFIG_NET_DSA_MV88E6XXX_GLOBAL2 is optional only if you use chips
that don't support the global2 area. Otherwise it is mandatory. So I
would update the commit message to not say "Additionally Global 2
register support is build-time optional", because it doesn't matter.

So I would simplify it to:

static inline bool mv88e6xxx_has_lag(struct mv88e6xxx_chip *chip)
{
	return !!chip->info->global2_addr;
}