[openwrt/openwrt] realtek: rtl838x: fix broadcast flooding with many multicast entries

[LEDE Commits]

robimarko pushed a commit to openwrt/openwrt.git, branch main:
https://git.openwrt.org/1b7fd8464c2b170d0862e0c19fff11fd8dc50611

commit 1b7fd8464c2b170d0862e0c19fff11fd8dc50611
Author: Linus Lüssing <linus.luessing at c0d3.blue>
AuthorDate: Wed May 7 02:50:11 2025 +0200

    realtek: rtl838x: fix broadcast flooding with many multicast entries
    
    When many multicast entries are installed broadcast flooding might
    potentially stop working for several ports. This is because the layer
    2 broadcast flood port mask index has the wrong offset. It should be
    9 bits, matching the 2^9 = 512 indexes on rtl838x, not 12.
    
    The wrong offset leads to L2_BC_FLD_PMSK being set to 504, not 511
    ((511 << 12) >> 9) & 511 = 504). So, as by default an unset PMSK
    is set to all ports, the issue would only become noticeable once
    many multicast entries are installed, causing the 504th entry to be set
    to something other than all ports.
    
    Fixing this by setting the offset to 9 bits, to correctly point to our
    511th reserved entry for all ports.
    
    Tested-on: ZyXEL GS1900-24HP v1
    
    Fixes: 28e972b2ea2f ("realtek: Configure initial L2 learning setup")
    Signed-off-by: Linus Lüssing <linus.luessing at c0d3.blue>
    Link: https://github.com/openwrt/openwrt/pull/18733
    Signed-off-by: Robert Marko <robimarko at gmail.com>
---
 target/linux/realtek/files-6.6/drivers/net/dsa/rtl83xx/rtl838x.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/linux/realtek/files-6.6/drivers/net/dsa/rtl83xx/rtl838x.c b/target/linux/realtek/files-6.6/drivers/net/dsa/rtl83xx/rtl838x.c
index f290e768de..f3969a3cc2 100644
--- a/target/linux/realtek/files-6.6/drivers/net/dsa/rtl83xx/rtl838x.c
+++ b/target/linux/realtek/files-6.6/drivers/net/dsa/rtl83xx/rtl838x.c
@@ -502,7 +502,7 @@ static void rtl838x_l2_learning_setup(void)
 	/* Set portmask for broadcast traffic and unknown unicast address flooding
 	 * to the reserved entry in the portmask table used also for
 	 * multicast flooding */
-	sw_w32(UNKNOWN_MC_PMASK << 12 | UNKNOWN_MC_PMASK, RTL838X_L2_FLD_PMSK);
+	sw_w32(UNKNOWN_MC_PMASK << 9 | UNKNOWN_MC_PMASK, RTL838X_L2_FLD_PMSK);
 
 	/* Enable learning constraint system-wide (bit 0), per-port (bit 1)
 	 * and per vlan (bit 2) */