Re: [PATCH] net: stmmac: set multicast filter to zero if feature is unsupported

From: Nikunj Kela
Date: Mon May 26 2025 - 12:17:26 EST



On 5/25/25 7:09 PM, Yanteng Si wrote:
在 5/24/25 6:19 AM, Nikunj Kela 写道:
Hash based multicast filtering is an optional feature. Currently,
driver overrides the value of multicast_filter_bins based on the hash
table size. If the feature is not supported, hash table size reads 0
however the value of multicast_filter_bins remains set to default
HASH_TABLE_SIZE which is incorrect. Let's override it to 0 if the
feature is unsupported.

Signed-off-by: Nikunj Kela <nikunj.kela@xxxxxxx>
---
  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 085c09039af4..ccea9f811a05 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -7241,6 +7241,9 @@ static int stmmac_hw_init(struct stmmac_priv *priv)
                      (BIT(priv->dma_cap.hash_tb_sz) << 5);
              priv->hw->mcast_bits_log2 =
ilog2(priv->hw->multicast_filter_bins);
+        } else {
+            priv->hw->multicast_filter_bins = 0;
+            priv->hw->mcast_bits_log2 = 0;
          }

I didn't read the code carefully, just did a simple search:

❯ grep -rn multicast_filter_bins drivers/net/
drivers/net/ethernet/stmicro/stmmac/common.h:611:    unsigned int multicast_filter_bins;
drivers/net/ethernet/stmicro/stmmac/dwmac-sophgo.c:26: plat_dat->multicast_filter_bins = 0;
***
drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c:512: plat->multicast_filter_bins = HASH_TABLE_SIZE;
***
drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c:536: &plat->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c:541: plat->multicast_filter_bins = dwmac1000_validate_mcast_bins(
drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c:542: &pdev->dev, plat->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c:523: mac->multicast_filter_bins = priv->plat->multicast_filter_bins;
drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c:527:    if (mac->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c:528: mac->mcast_bits_log2 = ilog2(mac->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:516: (netdev_mc_count(dev) > hw->multicast_filter_bins)) {
drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:1527: mac->multicast_filter_bins = priv->plat->multicast_filter_bins;
drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:1531:    if (mac->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:1532: mac->mcast_bits_log2 = ilog2(mac->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:1568: mac->multicast_filter_bins = priv->plat->multicast_filter_bins;
drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:1572:    if (mac->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:1573: mac->mcast_bits_log2 = ilog2(mac->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c:543:    if (netdev_mc_count(priv->dev) >= priv->hw->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c:633:    if (netdev_mc_count(priv->dev) >= priv->hw->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c:679:    if (netdev_mc_count(priv->dev) >= priv->hw->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/stmmac_pci.c:31: plat->multicast_filter_bins = HASH_TABLE_SIZE;
drivers/net/ethernet/stmicro/stmmac/stmmac_pci.c:84: plat->multicast_filter_bins = HASH_TABLE_SIZE;
drivers/net/ethernet/stmicro/stmmac/dwmac-loongson.c:98: plat->multicast_filter_bins = 256;
drivers/net/ethernet/stmicro/stmmac/dwmac-loongson.c:365: mac->multicast_filter_bins = priv->plat->multicast_filter_bins;
drivers/net/ethernet/stmicro/stmmac/dwmac-loongson.c:369:    if (mac->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/dwmac-loongson.c:370: mac->mcast_bits_log2 = ilog2(mac->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:7240: priv->hw->multicast_filter_bins =
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:7243: ilog2(priv->hw->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c:570: plat->multicast_filter_bins = HASH_TABLE_SIZE;
drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c:707: plat->multicast_filter_bins = HASH_TABLE_SIZE;
drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c:479: plat_dat->multicast_filter_bins = 0;
drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c:456:    int numhashregs = (hw->multicast_filter_bins >> 5);
drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c:485: (netdev_mc_count(dev) > hw->multicast_filter_bins)) {
drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c:1057: mac->multicast_filter_bins = priv->plat->multicast_filter_bins;
drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c:1061:    if (mac->multicast_filter_bins)
drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c:1062: mac->mcast_bits_log2 = ilog2(mac->multicast_filter_bins);
drivers/net/ethernet/stmicro/stmmac/dwmac-generic.c:43: plat_dat->multicast_filter_bins = HASH_TABLE_SIZE;

and

drivers/net/ethernet/stmicro/stmmac/common.h:265:#define HASH_TABLE_SIZE 64


From the search results, the default value of multicast_filter_bins
may be meaningful. And I think that even if some hardware does not
support this feature, it should still be overridden in its own directory.

There is a DT property 'snps,multicast-filter-bins' available to override the default value for a platform however this property is not taken into consideration in case of xgmac. That being said, stmmac_platform.c logic can be modified to extend the property use for xgmac also however the value will be overridden later based on hash table size read from the HW Feature register. So only zero value will be usable via DT in that case. Hence I thought of setting it to 0 in the else part of the code I modified in this patch. If you think I should extend the DT property for xgmac, I can modify the patch too.

Thanks,

-Nikunj



Thanks,
Yanteng