Re: [PATCH net v4 5/7] net: stmmac: dwmac4: Use the correct bufzise when the len is exactly 8K
From: Nicolai Buchwitz <hidden>
Date: 2026-09-18 12:25:39
Also in:
linux-arm-kernel, lkml
Hi Maxime On 17.9.2026 23:53, Maxime Chevallier wrote:
DMA bufsize selection isn't made on the MTU but the actual frame length, so including the L2 header. On DWMAC4, if the len is exactly BUF_SIZE_8KiB, the next larger size is incorrectly selected. Lets fix the comparison and while at it, rename the parameter from len to mtu.
Isn't it "[...] from mtu to len"?
quoted hunk ↗ jump to hunk
Fixes: c3efed5ad1b0 ("net: stmmac: Enable dwmac4 jumbo frame more than 8KiB"). Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com> --- drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c | 4 ++-- drivers/net/ethernet/stmicro/stmmac/hwif.h | 2 +- drivers/net/ethernet/stmicro/stmmac/ring_mode.c | 4 ++-- 3 files changed, 5 insertions(+), 5 deletions(-)diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.cb/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c index 2994df41ec2c..c6a8f8d73501 100644--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c@@ -474,11 +474,11 @@ static void dwmac4_set_sarc(struct dma_desc *p,u32 sarc_type) sarc_type)); } -static int set_16kib_bfsize(int mtu) +static int set_16kib_bfsize(int len) { int ret = 0; - if (unlikely(mtu >= BUF_SIZE_8KiB)) + if (unlikely(len > BUF_SIZE_8KiB))
Should we drop set_16kib_bfsize() instead? After 6/7 it looks to me like the same test as the first branch of stmmac_set_bfsize(). The caller ends up there anyway when it returns 0 and chain_mode_ops doesn't have it at all.
quoted hunk ↗ jump to hunk
ret = BUF_SIZE_16KiB; return ret; }diff --git a/drivers/net/ethernet/stmicro/stmmac/hwif.hb/drivers/net/ethernet/stmicro/stmmac/hwif.h index 04dafec021b4..de7aa6d28148 100644--- a/drivers/net/ethernet/stmicro/stmmac/hwif.h +++ b/drivers/net/ethernet/stmicro/stmmac/hwif.h@@ -540,7 +540,7 @@ struct stmmac_mode_ops { bool (*is_jumbo_frm)(unsigned int len, bool enh_desc); int (*jumbo_frm)(struct stmmac_tx_queue *tx_q, struct sk_buff *skb, int csum); - int (*set_16kib_bfsize)(int mtu); + int (*set_16kib_bfsize)(int len); void (*init_desc3)(struct dma_desc *p); void (*refill_desc3)(struct stmmac_rx_queue *rx_q, struct dma_desc*p); void (*clean_desc3)(struct stmmac_tx_queue *tx_q, struct dma_desc *p);diff --git a/drivers/net/ethernet/stmicro/stmmac/ring_mode.cb/drivers/net/ethernet/stmicro/stmmac/ring_mode.c index f7949419eb9f..d2f0c321661d 100644--- a/drivers/net/ethernet/stmicro/stmmac/ring_mode.c +++ b/drivers/net/ethernet/stmicro/stmmac/ring_mode.c@@ -124,10 +124,10 @@ static void clean_desc3(struct stmmac_tx_queue*tx_q, struct dma_desc *p) p->des3 = 0; } -static int set_16kib_bfsize(int mtu) +static int set_16kib_bfsize(int len) { int ret = 0; - if (unlikely(mtu > BUF_SIZE_8KiB)) + if (unlikely(len > BUF_SIZE_8KiB)) ret = BUF_SIZE_16KiB; return ret; }
regards Nicolai