Re: [PATCH v0] net: dsa: mv88e6xxx: Add FID map cache

Add a cached FID bitmap. This mitigates the need to
walk all VTU entries to find the next free FID.

Walk VTU once, then store read FID map into bitmap. Use
and manipulate this bitmap from now on, instead of re-reading
HW for the FID map.

The repeatedly VTU walks are costly can result in taking ~40 mins
if ~4000 vlans are added. Caching the FID map reduces this time
to <2 mins.

Signed-off-by: Aryan Srivastava <redacted>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 25 +++++++++++++++++++------
 drivers/net/dsa/mv88e6xxx/chip.h |  4 ++++
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index e5bac87941f6..91816e3e35ed 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c

@@ -1815,14 +1815,17 @@ int mv88e6xxx_fid_map(struct mv88e6xxx_chip *chip, unsigned long *fid_bitmap)
 
 static int mv88e6xxx_atu_new(struct mv88e6xxx_chip *chip, u16 *fid)
 {
-	DECLARE_BITMAP(fid_bitmap, MV88E6XXX_N_FID);
 	int err;
 
-	err = mv88e6xxx_fid_map(chip, fid_bitmap);
-	if (err)
-		return err;
+	if (!chip->fid_populated) {
+		err = mv88e6xxx_fid_map(chip, chip->fid_bitmap);
+		if (err)
+			return err;
 
-	*fid = find_first_zero_bit(fid_bitmap, MV88E6XXX_N_FID);
+		chip->fid_populated = true;
+	}
+
+	*fid = find_first_zero_bit(chip->fid_bitmap, MV88E6XXX_N_FID);
 	if (unlikely(*fid >= mv88e6xxx_num_databases(chip)))
 		return -ENOSPC;
 

@@ -2529,6 +2532,9 @@ static int mv88e6xxx_port_vlan_join(struct mv88e6xxx_chip *chip, int port,
 			 port, vid);
 	}
 
+	/* Record FID used in SW FID map */
+	bitmap_set(chip->fid_bitmap, vlan.fid, 1);
+